W  I  0     •      I  /  Z)  *    V?  ^  Issued  March  2G,  1914. 

HAWAII  AGRICULTURAL  EXPERIMENT  STATION, 

E.  V.  WILCOX,  Special  Agent  in  Charge. 


Bulletin  No.  32. 


THE  PAPAYA  IN  HAWAII 


BY 


J.  E.  HIGGINS, 

Hi   ticulturist, 


AND 


VALENTINE  S.  HOLT, 


Assistant  in  Horticulture. 


UNDER  THE  SUPERVISION  OF 
OFFICE    OF    EXPERIMENT    STATIONS, 

U.   S.    DEPARTMENT  OF  AGRICULTURE. 


WASHINGTON:  ""'Vr-W'1' 

GOVERNMENT  PRINTING  OFFICE. 
1914. 


/ 


Issued  March  26,  1914. 

HAWAII  AGRICULTURAL  EXPERIMENT  STATION, 

E.  V.  WILCOX,  Special  Agent  in  Charge. 


Bulletin  No.  32. 


THE  PAPAYA  IN  HAWAII 


BY 


J.  E.  HIGGINS, 

Horticulturist, 


VALEXTIXE  S.  HOLT, 

Assistant  in  Horticulture. 


UNDER  THE  SUPERVISION  OF 
OFFICE    OF    EXPERIMENT    STATIONS, 

U.   S.   DEPARTMENT  OF  AGRICULTURE. 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

1914. 


HAWAII   AGRICULTURAL   [EXPERIMENT    STATION,    HONOLULU. 

[Under  the  supervision  of  A.  C.  True,  Director  of  the  Office  of  Experiment  Stations,  United  States 

Department  of  Agriculture.] 

Walter  H.  Evans,  Chief  of  Division  of  Insular  Stations,  Office  of  Experiment  Stations. 

STATION  STAFF. 

E.  V.  Wilcox,  Special  Agent  in  Charge. 
J.  Edgar  Higgins,  Horticulturist. 

W.  P.  Kelley,  Chemist. 

C.  K.  McClelland,  Agronomist. 

D.  T.  Fullaway,  Entomologist. 

W.  T.  McGeorge,  Assistant  Chemist. 
Alice  R.  Thompson,  Assistant  Chemist. 
C.  J.  Hunn,  Assistant  Horticulturist. 
.  V.  S.  Holt,  Assistant  in  Horticulture. 
C.  A.  Sahr,  Assistant  in  Agronomy. 

F.  A.  Clowes,  Superintendent  Hawaii  Substations. 
W.  A.  Anderson,  Superintendent  Rubber  Substation. 
J.  deC.  Jerves,  Superintendent  Homestead  Substation. 
J.  K.  Clark,  Superintendent  Waipio  Substation. 
Geo.  Copp,  Superintendent  Kula  Substation. 

(2) 


LETTER  OF  TRANSMITTAL. 


Honolulu,  Hawaii,  June  30,  1913. 
Sir:  I  have  the  honor  to  submit  herewith  and  recommend  for 
publication,  as  Bulletin  No.  32  of  the  Hawaii  Agricultural  Experi- 
ment Station,  a  paper  on  the  Papaya  in  Hawaii,  by  J.  E.  Higgins, 
horticulturist,  and  V.  S.  Holt,  assistant  in  horticulture.  This  paper 
contains  the  results  of  investigations  at  this  station  and  a  considera- 
tion of  the  literature  of  the  subject  as  related  to  the  work  of  the 
station. 

Respectfully, 

E.  V.  Wilcox, 
Special  Agent  in  Charqe. 
Dr.  A.  C.  True, 

Director  Office  of  Experiment  Stations, 

TJ.  S.  Department  of  Agriculture,  Washington,  D.  C. 

Publication  recommended. 
A.  C.  True,  Director. 

Publication  authorized. 

D.  F.  Houston,  Secretary  of  Agriculture. 

(3) 


CONTEXTS 


Page. 

Introduction 7 

Part  I.  Culture  and  uses 7 

Natural  requirements 7 

Propagation 8 

Transplanting  large  trees 9 

Irrigation 10 

Fertilizers 10 

Pruning  and  change  of  sex 10 

Thinning  the  fruits 11 

Artificial  feeding 11 

Renewing  the  plantings 11 

The  fruit  crop 11 

Varieties 12 

The  papaya  as  a  food 13 

Medicinal  and  other  uses 15 

Papain 16 

Collecting  and  preparing  the  juice : 17 

Part  II.  Breeding  of  papaya 18 

Botanical  names 18 

Common  names 18 

Botanical  relationships 19 

Descriptions  of  forms  of  papaya 19 

Summary  of  forms 23 

Significance  of  the  forms 25 

Change  of  sex 25 

The  female  in  sex  change 27 

Inheritance  of  change  of  sex 28 

Origin  of  different  forms 28 

Origin  of  the  dioecious  Carica  papaya 31 

Breeding  within  the  dioecious  forms 32 

Breeding  the  hermaphrodite  forms 34 

Hermaphroditism  in  Lychnis  dioica 35 

Breeding  within  the  andromoncecious  forms 36 

Crossing  the  different  forms 36 

Possibilities  and  limitations 36 

Combining  dioecious  with  hermaphrodite  forms 38 

Stocks  not  showing  any  fertilization 40 

Parthenocarpy 40 

Parthenogenesis 41 

Hybridization  of  Carica 41 

An  attempt  to  breed  a  hermaphrodite  papaya 42 

Ideals  in  breeding  the  papaya 42 

Insect  pests.    By  D.  T.  Fullaway 44 

(5) 


ILLUSTRATIONS. 


Page. 

Plate  I.  Papaya  orchard  in  which  nearly  every  tree  is  bearing  fruit 16 

II.  Crates  for  papayas 16 

III.  Pistillate  papaya  tree  and  flower  of  the  dioecious  type 16 

IV.  Fig.  1. — Male  papaya  tree.     Fig.  2. — Correse  tree  with  a  few  fruits; 

staminate  flowers  to  the  right 16 

V.  Fig.  1. — Correse  tree  bearing  only  two  or  three  fruits.     Fig.  2. — Cor- 

rea?  tree  bearing  many  fruits 24 

VI.  Elongata  tree  and  fruit 24 

VII.  Fig.  1. — Elongata  tree  with  long  bare  spaces,  and  elongata  her- 
maphrodite flower.     Fig.  2. — Sterile  hermaphrodite  tree 24 

VIII.  Elongata  and  pentandria  fruits  on  the  same  tree,  pentandria  flowers, 

and  a  fruit  within  a  fruit 24 

IX.  Fig.  1. — Intermediate  forms.     Fig.  2. — An  example  of  parthenocarpic 

development 24 

X.  Fig.  1 . — A  papaya  tree  changed  from  male  to  female  by  pruning.     Fig. 

2 . — Pistillate  flower  with  elongata  form  of  ovary 24 

(6) 


THE  PAPAYA  IN  HAWAII 


INTRODUCTION. 

Excepting  the  banana,  there  is  no  fruit  grown  in  the  Hawaiian 
Islands  that  means  more  to  the  people  of  this  Territory  than  the 
papaya,  if  measured  in  terms  of  the  comfort  and  enjoyment  furnished 
to  the  people  as  a  whole.  The  papaya  is  the  almost  universal  breakfast 
fruit  in  Hawaii,  enjoyed  alike  by  rich  and  poor,  and  is  recognized  as 
one  of  the  most  wholesome  fruits  wherever  it  abounds.  It  grows  so 
readily,  with  so  little  care,  in  such  variety  of  soils  and  conditions, 
with  no  serious  diseases  or  insect  pests;  it  occupies  so  little  space  and 
matures  a  crop  so  quickly  that  it  is  to  be  found  in  nearly  every  door- 
yard  and  garden.  The  taste  for  the  papaya  seldom  needs  to  be  ac- 
quired, although  appreciation  for  it  increases  with  familiarity,  and 
there  are  few  fruits  which  can  be  indulged  in  so  regularly  without 
wearying  the  taste.  All  this  applies  to  the  really  good  papaya,  for 
there  are  few  fruits  which  vary  more  widely  in  flavor  than  these. 

Because  of  its  importance  as  a  home  fruit  as  well  as  one  for  local 
market  in  Hawaii;  because  of  its  possibilities  in  manufactured  pro- 
ducts, and,  for  some  countries,  in  export;  because  of  the  need  of 
establishing  good  varieties  that  can  be  depended  upon  to  reproduce 
themselves;  because  of  inquiries  relating  to  methods  of  culture  and 
to  the  possibilities  of  papain  production;  and  because  of  the  import- 
ance of  certain  scientific  problems  which  are  referred  to  in  the  last 
part  of  this  publication,  the  Hawaii  Experiment  Station  has  been 
pursuing  certain  investigations  of  this  plant  and  offers  this  paper  as  a 
contribution  to  the  limited  literature  of    the  papaya. 

PART  I.   CULTURE  AND  USES. 

NATURAL   REQUIREMENTS. 

The  papaya  is  a  tropical  plant  and  does  not  prosper  under  any 
other  than  tropical  conditions.  Just  outside  the  Tropics  it  is  grown  as 
a  beautiful  ornamental  that  occasionally  yields  fruit,  but  it  is  never  a 
success  as  a  fruit  producer.  In  Hawaii  it  thrives  best  below  1,200 
feet  altitude,  luxuriating  and  producing  its  best  fruits  in  the  warmest 
localities.  The  effect  of  the  lack  of  heat  in  the  cool  season  is  marked 
by  a  retarding  of  the  process  of  maturing  and  ripening  fruit  and  to 

23558°— 14 2  (7) 


8 

a  less  degree  by  a  slower  growth  and  the  setting  of  less  fruit.  Fruit 
produced  at  high  altitudes  or  that  maturing  during  very  cool  weather 
is  frequently  inferior  in  flavor.  Reference  will  be  made  later  to  the 
tendency  of  cold  weather  to  produce  a  fruiting  condition  in  the  male 
tree. 

In  regard  to  rainfall  and  moisture  requirements,  the  plant  is  able  to 
adapt  itself  to  a  wide  range  of  conditions,  and  when  established  suffers 
much  less  from  a  shortage  of  water  than  the  orange  or  the  avocado, 
but  makes  beneficial  use  of  large  amounts  if  supplied.  Yet  withal, 
it  is  one  of  the  most  insistent  plants  in  matters  of  drainage.  In 
water-logged  soils  the  papaya  makes  a  spindling  growth  and  drops 
its  lower  leaves  prematurely  while  the  remaining  foliage  becomes 
yellow,  the  whole  plant  indicating  an  unhealthy  condition. 

There  are  few,  if  any,  soils  in  which  the  papaya  will  not  grow  if  aera- 
tion and  drainage  are  adequately  supplied.  Most  of  the  plantings  at 
this  station  are  upon  soils  regarded  as  unsuitable  for  other  fruit  trees, 
and  upon  which  the  avocado  is  a  failure.  It  is  true  that  these  soils 
are  fairly  well  supplied  with  potash,  being  black  sand  or  volcanic  ash 
in  the  early  stages  of  disintegration.  They  are  very  porous,  per- 
mitting a  perfect  drainage  and  aeration.  Rich  soils  give  correspond- 
ingly better  and  more  permanent  results  if  they  permit  of  the  free 
passage  of  water  and  the  entrance  of  air. 

PROPAGATION. 

The  papaya  is  usually  propagated  by  seeds.  Very  little  systematic 
effort  has  been  made  to  establish  varieties  that  can  be  depended  upon 
to  reproduce  their  characters,  as  has  been  done  with  so  many  culti- 
vated plants.  This  matter  is  more  fully  discussed  in  the  second  part 
of  this  bulletin,  but  it  may  be  here  stated  that  judicious  selection  is 
as  promising  of  results  as  with  other  plants,  and,  therefore,  seeds  from 
good  trees  only  should  be  planted.  This  station  has  been  breeding 
papayas  for  a  short  time  and  while  seed  can  not  yet  be  regarded  as 
wholly  dependable  to  produce  the  variety  some  seed  is  available  in 
small  quantities  to  those  who  have  suitable  facilities  for  its  growth. 

The  seed  is  taken  from  the  fruit,  washed  to  remove  the  outer 
gelatinous  coat,  and  dried.  It  may  then  be  stored  in  glass  bottles  if 
it  is  not  desired  to  plant  it  at  once,  and  it  will  retain  its  viability  for 
several  years  if  not  attacked  by  insects.  It  is  best  to  plant  the  seed 
in  a  well-drained,  porous  soil  in  flats  or  boxes,  covering  them  about 
a  half  inch  deep.  In  from  2  to  6  weeks  the  seedlings  should  appear, 
germination  being  hastened  by  heat.  In  the  open  in  cool  weather 
the  time  will  not  be  less  than  a  month,  but  in  a  warm  greenhouse  it 
may  be  shortened  to  2  weeks.  In  about  a  month  after  germination 
the  seedlings  should  be  large  enough  to  be  transferred  to  pots  in  which 
they  should  remain  for  another  month  before  being  placed  in  the 


9 

orchard  or  garden.  Such  plants  should  not  wilt  when  they  are  set 
out. 

In  planting,  holes  2J  feet  in  each  dimension  should  be  dug  and 
refilled.  If  the  trees  are  to  be  planted  in  a  lawn,  holes  3  J  feet  in  diame- 
ter will  be  better.  The  distances  between  trees  should  be  about  10 
feet  in  each  direction.  Shading  is  not  usually  necessary  with  plants 
hardened  in  pots,  but  in  a  windy  locality  some  protection  from  exces- 
sive loss  of  moisture  is  desirable.  At  this  time,  particularly  in  the 
winter  season,  precautions  should  be  taken  to  prevent  the  destruction 
of  the  plants  by  cutworms  (see  p.  44). 

Recently  considerable  attention  has  been  given  to  propagating 
the  papaya  by  asexual  means.  For  some  time  cuttings  from  the 
young  shoots  on  the  side  of  the  tree  have  been  made  to  form  roots 
under  suitable  conditions  of  temperature  and  humidity,  but  this 
has  not  been  regarded  as  a  practical  means  for  general  propagation. 
Prof.  P.  H.  Rolfs  was  probably  the  first  to  apply  successfully  any 
form  of  grafting  to  this  species.  His  method,  as  reported  in  a  letter 
to  Dr.  E.  V.  Wilcox  of  this  station,  was  inarching,  the  experiments 
having  been  conducted  when  Prof.  Rolfs  was  in  charge  of  the  Sub- 
tropical Laboratory  of  the  U.  S.  Department  of  Agriculture,  at  Miami, 
Fla.  "The  inarching  was  made  by  cutting  away  a  considerable  por- 
tion of  the  branch,  as  well  as  a  considerable  portion  of  the  stock. 
The  two  were  then  brought  together  and  held  firmly  in  place  with 
raffia.  In  the  course  of  a  few  weeks  the  two  had  made  a  very  good 
union.' ' 

Credit  is  due  to  Mr.  David  Fairchild  and  Mr.  Edward  Simmonds 
for  having  first  applied  cleft  grafting  to  the  papaya.  In  a  recent 
circular  *  their  method  is  described,  which  consists  in  applying  scions 
from  side  shoots  to  seedlings  about  two  months  old,  or  less.  The 
stock  is  cut  off  with  a  horizontal  cut,  and  the  usual  cleft  is  made  with 
a  very  sharp  knife. 

Both  of  these  methods  have  been  tried  at  the  Hawaii  station,  and 
successful  unions  have  been  effected.  It  seems  not  improbable  that 
some  of  these  methods  of  asexual  propagation  may  prove  valuable 
in  prolonging  the  existence  of  superior  trees  for  breeding  purposes. 
It  is  claimed  that  trees  so  propagated  fruit  more  quickly  than  seed- 
lings, which  is  in  accord  with  the  general  principle  of  budded  and 
grafted  stock.  This  would  be  an  advantage  in  subtropical  countries 
where  a  few  weeks  may  make  a  great  difference  in  the  fruiting  season. 

TRANSPLANTING   LARGE   TREES. 

When  necessity  demands,  it  is  possible  to  move  quite  large  trees. 
There  are  reports  of  trees  having  been  moved  when  two  or  three  years 
old.     The  writers  have  not  had  occasion  to  attempt  the  transplanting 

i  U.  S.  Dept.  Agr.,  Bur.  Plant  Indus.  Circ.  119. 


10 

of  papaya  trees  more  than  5  or  6  feet  high.  These  have  been  success- 
fully moved  on  several  occasions  during  the  last  12  years  by  taking 
up  as  much  as  possible  of  the  root  system  intact  and  cutting  off  the 
leaf  blades,  except  those  at  the  top  not  fully  developed,  a  part  of  each 
petiole  or  footstalk  being  left  attached  to  the  trunk. 

IRRIGATION. 

While  the  papaya  will  produce  good  fruit  with  a  quite  limited 
supply  of  water,  it  responds  freely  to  liberal  irrigation  on  well- 
drained  soils,  and  under  such  conditions  yields  larger  fruits  and 
heavier  crops.  It  is  impossible  to  state  any  rule  which  can  govern 
the  amount  of  irrigation  under  the  widely  different  conditions  exist- 
ing, but  in  general  it  may  be  said  that  less  water  than  is  required  for 
the  orange  will  suffice.  When  the  young  plants  are  set  out  they  re- 
quire watering  every  day  or  two  for  a  few  weeks,  because  the  surface 
soil  in  which  are  the  roots  dries  out  very  rapidly.  In  the  few  small 
plantations  in  the  dry  districts  near  Honolulu  water  is  applied  to 
established  trees  in  ditches  or  depressions  between  the  rows. 

FERTILIZERS. 

No  exact  data  are  available  to  show  the  actual  fertilizer  require- 
ments of  the  plants.  This  station  has  used  successfully  on  young 
trees  the  following  fertilizer  forftiula: 

Pounds. 

Superphosphate  (acid  phosphate) 800 

High  grade  sulphate  of  potash 315 

Nitrate  of  soda 250 

Sulphate  of  ammonia 190 

Flack  sand  (volcanic  ash) 445 

Total 2, 000 

This  has  been  applied  at  the  rate  of  1  pound  per  tree  at  planting 
time,  thoroughly  mixed  with  the  soil  in  the  hole  prepared  for  the 
tree,  and  as  a  surface  dressing  six  months  later. 

PRUNING   AND   CHANGE   OF    SEX. 

There  is  little  necessity  for  pruning  papaya  trees.  Some  plants 
show  a  tendency  to  send  out  side  shoots,  and  it  is  advisable  to  remove 
these  or  the  nourishment  will  be  diverted  from  the  fruit  crop  on  the 
main  trunk.  When  the  latter  has  borne  for  two  or  three  years  it 
may  be  cut  down,  and  some  of  the  side  shoots  may  be  allowed  to 
form  a  new  top,  which  will  continue  the  bearing  life  of  the  tree  and 
produce  easily  accessible  fruits. 

Changing  the  sex  of  a  male  tree  has  at  times  been  brought  about 
by  severe  pruning.  Removing  the  terminal  bud  or  even  cutting  off 
the  whole  top  below  the  leaves  has  been  known  to  bring  about  this 


11 

change  (see  p.  26),  but  such  treatment  can  not  be  depended  upon  to 
do  so. 

In  Plate  X,  figure  1 ,  is  shown  a  staminate  tree  which,  so  far  as 
observed,  produced  no  fruit-bearing  flowers.  It  was  cut  to  a  stump 
about  6  or  8  feet  high,  and  soon  sent  out  side  branches  upon  which 
only  pistillate  (female)  flowers  have  been  found. 

THINNING   THE   FRUITS. 

There  is  a  great  variation  in  productivity  among  papayas.  In 
some  there  is  a  cluster  of  several  fruits  in  the  axil  of  every  leaf, 
while  in  others  only  a  single  fruit  is  to  be  found  at  each  axil,  and 
still  others  may  have  only  a  few  fruits  scattered  up  and  down  the 
trunk.  When  the  fruits  are  borne  in  clusters  it  frequently  becomes 
necessary  to  thin  them  out  because  there  is  not  sufficient  space  for 
their  development,  and  if  not  thinned  they  crowd  each  other  into 
distorted  shapes.  The  thinning  may  be  easily  and  quickly  per- 
formed with  a  knife  when  the  fruits  are  young. 

ARTIFICIAL   FEEDING. 

A  number  of  tropical  agricultural  journals  have  reported  what 
purports  to  be  an  instance  of  artificial  nutrition  in  the  papaya, 
credited  to  Mr.  Jesse,  of  Jolo,  Philippine  Islands.1  In  this  treat- 
ment it  is  said  that  a  hole  is  bored  in  the  trunk  about  6  inches  from 
the  ground,  1  inch  deep,  and  of  a  diameter  "  slightly  larger  than  the 
red  rubber  tubing  obtainable  at  drug  stores."  Fill  a  quart  bottle 
half  full  of  sugar  and  dissolve  in  water.  When  the  sugar  is  dissolved, 
connect  the  bottle  with  the  hole  in  the  tree  by  the  rubber  tubing. 
In  24  hours  the  tree  is  supposed  to  have  absorbed  the  contents  of  the 
bottle. 

RENEWING   THE    PLANTINGS. 

Papaya  trees  are  of  short  life.  Specimens  have  been  known  to 
continue  in  bearing  for  15  years,  but  the  period  of  profitable  pro- 
ductivity is  usually  not  over  3  or  4  years.  Trees  can  be  grown  so 
easily  and  so  quickly  that  it  is  the  custom  to  renew  the  plantings 
often. 

THE   FRUIT   CROP. 

The  first  ripe  fruits  may  be  expected  in  about  a  year  from  the  time 
when  the  plants  are  set  in  the  orchard  or  garden,  and  thereafter  fruits 
and  flowers  in  all  stages  of  development  may  be  in  evidence  at  all 
times  of  the  year.  In  the  cool  season  the  fruits  are  slow  in  ripening, 
thus  causing  a  short  crop  and  high  prices  for  a  month  or  two.  At 
this  time  the  growers  often  receive  3  to  3}  cents  per  pound  for  fruit 
which  in  summer  would  not  bring  more  than  1  or  1  \  cents. 

i  Trop.  Agr.  and  Mag.  Ceylon  Agr.  Soc.,  37  (1911),  No.  1,  pp.  32,  33. 


12 

Papayas  for  market  should  be  picked  very  soon  after  they  show 
the  first  yellowing.  In  the  case  of  some  trees,  particularly  of  the  long 
fruited  varieties,  the  necessary  maturity  is  indicated  by  light  green 
color.  Certain  varieties  become  ripe  enough  for  serving  while  showing 
little  yellow  coloring.  Papayas  are  so  large  and  heavy  that  it  is 
difficult  to  get  them  safely  to  the  consumer  if  they  have  begun  to 
soften  when  picked.  Great  care  is  necessary  to  avoid  bruising.  For 
local  market  they  may  be  carried  on  the  body  of  a  spring  wagon 
provided  with  straw,  excelsior,  or  similar  material,  or,  for  more  than 
one  tier  of  fruit,  racks  may  be  provided. 

In  the  fruit-marketing  investigations  conducted  by  this  station  it 
was  found  that  papayas  can  be  shipped  long  distances.  They  were 
taken  to  San  Francisco  with  very  small  losses  and  were  marketed  in 
small  quantities  from  San  Francisco,  in  Portland,  Seattle,  Tacoma, 
and  Vancouver,  B.  C.1  The  chief  results  may  be  summarized  as 
follows: 

Fruits,  preferably  of  the  long  varieties,  should  be  gathered  when 
they  show  the  first  indications  of  ripening.  They  should  be  wrapped 
in  paper  and  surrounded  by  a  sleeve  or  cylinder  of  crimped  strawboard 
before  being  placed  in  the  single-tier  crates  in  which  they  are  shipped. 
It  is  important  to  get  them  into  refrigeration  as  soon  as  possible. 
The  crates  used  in  these  experiments  are  illustrated  in  Plate  II. 
They  proved  satisfactory  in  dimensions  but  could  be  made  of  lighter 
material. 

It  is  well  known  locally  that  papayas,  with  all  other  fruits  from 
Hawaii,  except  bananas  and  pineapples,  are  now  prevented  from 
being  shipped  to  California  because  of  the  prevalence  of  the  Mediter- 
ranean fruit  fly  in  these  islands.  These  directions  therefore  are 
repeated  at  present,  not  for  any  local  applicability,  but  for  whatever 
use  they  may  be  in  other  tropical  countries. 

VARIETIES. 

Strictly  speaking  there  are  few,  if  any,  varieties  of  papaya.  A  vari- 
ety, in  the  case  of  seed-propagated  plants,  is  a  described  and  named 
form,  having  certain  well-recognized  characters  which  are  reproduced 
in  the  offspring  with  a  reasonable  degree  of  accuracy  and  usually 
maintained  by  artificial  pollination  or  by  segregation  to  prevent 
crossing  with  pollen  from  other  varieties  or  species.  Such  work,  so 
far  as  has  been  learned,  has  not  been  conducted  with  the  papaya  long 
enough  to  justify  the  naming  of  any  form  and  thus  giving  to  it  the 
rank  of  a  variety.  This  station  has  now  in  hand  a  line  of  selections 
and  close  pollinations  which  it  is  hoped  may  yield  some  forms  suffi- 
ciently distinct  and  stable  to  merit  naming.  At  present  the  station 
forms  are  designated  by  numbers  only. 

i  Hawaii  Sta.  Bui.  14. 


13 

In  a  less  exact  sense  such  terms  as  "long  variety"  and  "round 
variety"  are  sometimes  used.  These  are  intended  to  designate 
respectively  the  perfect-flowered  form  in  which  both  male  and  female 
organs  are  in  the  same  flower,  and  the  commoner  form  in  which  there 
are  male  and  female  trees.  This  subject  will  be  discussed  more  at 
length  in  the  last  part  of  this  bulletin.  For  those  who  may  not  care 
for  the  more  technical  part  of  the  subject,  it  may  be  said  that  the 
present  endeavor  is  toward  the  former  type  and  the  elimination  of 
the  male  trees  which  in  the  latter  type  frequently  form  75  to  85  per 
cent  of  the  trees,  and  are  indistinguishable  from  the  females  until 
flowering  time,  and  thus  are  wasteful  of  space  and  time.  Seeds  of  the 
long  variety  generally  produce  a  very  large  majority  of  fruit-bearing 
treos.  Plate  I  shows  a  view  in  an  orchard  in  which  nearly  every  tree 
is  bearing  fruit. 

THE    PAPAYA   AS   A   FOOD. 

Perhaps  the  most  frequent  use  of  the  papaya  is  as  food,  although 
almost  all  parts  of  the  plant  are  utilized  in  some  way. 

The  general  composition  of  the  papaya  fruit  is  shown  by  the  fol- 
lowing analysis : * 

Per  cent. 

Water 90.  75 

Protein 80 

Fat 10 

Fiber 1.  09 

Nitrogen-free  extract 6.  32 

Ash .94 

Reference  has  been  made  above  to  the  nearly  universal  use  of  the 
ripe  papaya  in  the  Tropics  as  a  breakfast  fruit.  For  this  purpose 
it  is  cut  lengthwise  into  portions  and  the  seeds  removed.  The 
placenta  with  the  seeds  attached  may  often  be  removed  without 
scraping  the  flesh,  which  is  thus  left  in  the  most  attractive  form  for 
serving.  Many  prefer  the  choicest  fruits  without  other  flavoring  of  any 
kind,  but  a  little  juice  of  the  lemon  or  the  lime  is  a  favorite  accom- 
paniment, while  a  few  prefer  salt  and  pepper  or  even  sugar.  The 
green  fruit  when  fully  grown  may  be  cooked  as  summer  squash,  for 
which  it  affords  a  very  good  substitute.  The  ripe  fruit  is  used  in 
making  papaya  glace. 

The  following  recipes,  taken  from  a  book  recently  published,  give 
some  directions  for  the  use  of  this  fruit : 2 

China  Orange  and  Papaya  Makmaladk,  No.  1. 

To  1  measure  papaya  allow  \  measure  China  oranges.  Wash  oranges  well.  Squeeze 
out  seeds  and  juice.  Put  skins  through  a  meat  chopper  and  add  to  the  juice,  strained 
free  from  seeds.  Add  papaya  pulp  cut  in  small  pieces  and  boil  all  together;  then 
add  as  much  sugar  as  pulp.     Boil  again  for  15  or  20  minutes. 

i  Maine  Sta.  Bui 

*  Jessie  C.  Turner  and  Agnes  B.  Alexander.    How  to  Use  Hawaiian  Fruits.    Honolulu,  1910,  pp.  17, 42, 43. 


14 

China  Orange  and  Papaya  Marmalade,  No.  2. 

To  6  cups  papaya  cut  in  small  pieces  add  J  cup  China  orange  juice.  Boil  15  min- 
utes and  add  half  as  much  sugar  as  pulp.     Boil  again  for  15  or  20  minutes. 

Stewed  Papaya,  No.  1. 
2  cups  diced  papaya  i  cup  water 

i  cup  sugar  Juice  2  lemons 

Cut  papaya  in  dice  and  stew  with  sugar,  water,  and  lemon  juice  \  hour.  Serve 
in  sherbet  glasses  as  a  first  course  for  luncheon,  or  a  dessert.  Can  use  4  China 
oranges  in  place  of  lemons. 

Stewed  Papaya,  No.  2. 

Cook  in  the  same  manner  as  No.  1,  with  \  cup  sugar  and  only  enough  water  to  keep 
from  burning.     Serve  as  vegetable. 

Baked  Papaya. 

Cut  papaya  in  halves  lengthwise.  Add  a  little  sugar  and  China  orange,  lime,  or 
lemon  juice;  or  a  little  cinnamon  in  place  of  the  juice.  Bake  20  minutes,  and  serve 
immediately  on  taking  from  the  oven.     This  is  a  vegetable. 

Papaya  Pickle. 

Make  sirup  of  1  measure  sugar  and  \  measure  vinegar.  Add  a  few  whole  cloves 
and  pepper  corns  and  2  measures  of  half-ripe  papaya  cut  into  small  pieces.  Boil 
until  tender. 

Papaya  and  Ginger. 

Make  a  sirup  of  1  measure  ginger,  \  measure  water,  some  finely  sliced  dried  ginger, 
and  a  few  slices  of  lemon.  Add  2  measures  half-ripe  papaya  sliced  lengthwise,  which 
has  been  previously  simmered  in  water  until  clear,  but  not  broken. 

Papaya  Cocktail. 

Cut  papaya  in  dice  and  serve  in  glasses  with  cocktail  sauce  and  chipped  ice. 

Or  serve  with  China  orange,  lemon,  or  lime  juice,  and  little  sugar  in  same  manner. 

Papaya  Salad,  No.  1. 

On  a  strip  of  peeled  papaya  lay  small  bits  of  pomelo  and  orange.  Serve  with  may- 
onnaise on  separate  plates,  and  garnish  each  with  one  or  two  nasturtiums  and  leaves. 

Papaya  Salad,  No.  2. 

Cut  papaya  in  cubes  and  add  8  small  Chinese  onions  and  5  pieces  green  celery 
chopped  fine.     Serve  with  boiled  dressing. 

Papaya  Whip. 

To  1^  cups  papaya  pulp  add  juice  1  lemon,  \  cup  sugar,  and  beat  into  2  stiffly 
whipped  whites  of  eggs. 

Papaya  Jelly. 
\  box  gelatine  1  cup  boiling  water 

\  cup  cold  water  1  cup  papaya  pulp 

Juice  1  lemon  \  cup  sugar 

Soak  gelatine  in  the  cold  water  5  minutes.  Dissolve  the  sugar  in  the  boiling 
water;  add  the  gelatine  and  strain.  When  cool,  add  the  papaya  and  lemon  juice. 
Place  on  ice  to  harden. 


15 

Papaya  Pie. 
2  eggs  1  cup  sugar 

1  cup  papaya  pulp  Juice  \  lemon 

\  cup  butter 
Make  a  bottom  pie  crust  and  bake.     Cream  butter  and  sugar.     Add  beaten  eggs, 
lemon  juice,  and  papaya.     Pour  into  pie  crust  and  bake.     Make  a  meringue  of 
whites  of  cgffs  and  2  tablespoonfuls  sugar.     Place  on  pie  and  brown  in  oven. 

Papaya  Sherbet. 

Mix  4  cups  papaya  pulp  with  2  cups  sugar  and  juice  of  2  lemons,  and  freeze. 

MEDICINAL   AND   OTHER   USES. 

Papaya  bark  is  used  in  the  manufacture  of  ropes.  Nearly  all  parts 
of  the  plant  are  credited  with  some  medicinal  value.  The  roots  afford 
a  nerve  tonic.  The  seeds  are  said  to  be  anthelmintic,  emmenagogic, 
and  carminative.  They  are  also  eaten  as  a  delicacy  and  as  a  quencher 
of  thirst.  The  ripe  fruit  finds  a  place  as  an  ingredient  in  certain  sirups 
'and  elixirs,  which  are  said  to  be  expectorant,  sedative,  and  tonic. 

The  most  important  medicinal  property  of  the  plant  is  found  in  the 
milky  juice.  This  is  used  by  the  natives  of  the  Tropics  in  the  treat- 
ment of  eczema,  warts,  intestinal  worms,  ulcers,  and  many  kinds  of 
foul  sores,  in  diphtheria  to  dissolve  the  false  membrane  in  the  throat, 
and  for  numerous  other  ailments. 

The  ripe  fruit  is  used  as  a  cosmetic,  a  slice  of  it  being  rubbed  upon 
the  skin  to  remove  freckles  and  other  blemishes.  The  green  fruit  and 
the  leaves  are  employed  as  soap  to  remove  stains  from  clothing. 

Xo  single  use  of  the  papaya,  except  for  food,  is  so  common  in  the 
Tropics  as  that  of  the  milky  juice  in  rendering  tough  meat  tender. 
For  this  purpose  a  slice  of  the  green  fruit,  rich  in  juice,  is  rubbed  over 
the  tough  flesh,  or  the  latter  is  dipped  for  a  few  minutes  in  a  solution 
of  the  juice.  Sometimes  a  piece  of  the  green  fruit  is  put  in  the  water 
in  which  the  meat  is  boiled. 

Another  practice  is  to  wrap  the  meat  in  papaya  leaves  overnight,  or 
even  to  hang  it  in  the  papaya  tree.  The  feeding  of  green  papayas  to 
hogs  is  reported  to  make  the  pork  tender.  Some  of  these  practices 
are  of  doubtful  efficacy.  Some  writers  recommend  mixing  ginger 
with  the  juice  when  it  is  to  be  applied  to  meat. 
23558°— 14 3 


16 

PAPAIN. 

Most  of  the  effects  of  papaya  juice  referred  to  above  are  due  to  the 
presence  in  the  juice  of  an  active  principle  which  has  been  named 
"papain."1  This  was  first  investigated  by  Wurtz  and  Bouchut,  in 
1879.2  It  may  be  separated  from  the  juice  by  means  of  alcohol,  and 
either  the  juice  itself  or  the  separated  ferment  is  now  well  known  to 
possess  the  power  of  digesting  proteids,3 

The  medicinal  use  of  this  ferment  has  grown  to  considerable  pro- 
portions and  has  given  rise  to  a  not  insignificant  trade  in  papaya 
juice.  Exact  data  of  imports  of  dried  papaya  juice  in  the  United 
States  are  not  available,  but  those  closely  in  touch  with  the  manufac- 
turing end  of  the  business  estimate  the  value  of  the  importations  at 
about  $75,000  to  $80,000.  The  price  paid  varies  from  $1.50  to  $3  per 
pound.  The  product  is  often  adulterated  and  also  may  in  part  lose  its 
efficacy  by  careless  methods  of  preparation.  It  therefore  is  bought 
on  sample  tested  to  determine  its  digestive  properties.  The  term 
"papain,"  which  primarily  refers  to  the  ferment,  has  been  extended 
in  its  use  and  now  is  applied  to  the  dried  juice  also,  either  crude  or  in 
various  stages  of  manufacture. 

The  chief  sources  of  supply  for  the  American  trade  are  the  West 
Indies  and  Ceylon.  Some  years  ago  Jamaica  maintained  an  industry 
of  some  importance  in  collecting  and  preparing  the  juice  for  market, 
but  it  is  no  longer  continued.  Later  the  business  grew  up  in  the 
island  of  Montserrat,  which  became  the  chief  producer  in  the  West 
Indies,  whose  papain  brought  a  much  higher  price  than  the  average 
product  from  Ceylon.  Opinion  among  large  manufacturers  seems 
to  be  divided  on  the  question  of  the  present  relation  of  supply  and 
demand,  some  stating  that  the  consumption  of  the  drug  is  on  the 
increase  and  the  prospect  good  for  marketing  larger  quantities,  while 
others  affirm  that  the  only  means  of  extending  the  market  now  would 

i  Written  also  papain  and  papaine. 

2  Compt.  Rend.  Acad.  Sci.  [Paris],  89  (1879),  p.  425.     Wurte,  ibid.,  90  (1880),  p.  1379;  91  (1880),  p.  787. 

»  Readers  interested  in  a  study  of  the  chemical  and  physiological  properties  of  papain  may  consult  the 
following  references: 

Amer.  Jour.  Med.  Sci.,  n.  ser.,  124  (1902),  pp.  310-318. 

Amer.  Jour.  Pharm.,73  (1901),  Nos.  6,  p.  272;  7,  p.  336;  8,  p.  383.  Reprinted  in  Bui.  Dept.  Agr. 
Jamaica,  1  (1903),  No.  8,  p.  181;  2  (1904),  Nos.  4,  p.  84;  5,  p.  113;  8,  p.  178. 

Amer.  Jour  Physiol.,  1  (1898),  No.  2,  pp.  255-276. 

Ann.  Bot.  [London],  17  (1903),  pp.  237-264;  19  (1905),  pp.  149-162. 

Compt.  Rend.  Acad.  Sci.  [Paris],  148  (1909),  No.  8,  pp.  497-500. 

Compt.  Rend.  Soc.  Biol.  [Paris],  66  (1909),  Nos.  5,  p.  227;  8,  p.  366. 

Jour.  Biol.  Chem.,  8  (1910),  No.  3,  pp.  177-213. 

Jour.  Physiol.,  5  (1885),  pp.  213-230;  6  (1885),  pp.  336-360. 

London  Med.  Rec,  3  (1875),  p.  253. 

Pharm.  Jour,  and  Trans.,  3.  ser.,  10  (1879),  pp.  343-346,  383-386. 

Pharm.  Jour.  [London],  4.  ser.,  2  (1896),  p.  182. 

Trans.  Conn.  Acad.  Arts  and  Sci.,  11  (1901),  pt.  1,  pp.  1-14. 

U.  S.  Dispensatory.    Philadelphia,  1907, 19.  ed.,  pp.  1603, 1604. 

West  Indian  Bui.,  4  (1903),  No.  1,  pp.  22-28. 

Christy,  T.  New  Commercial  Plants  and  Drugs.  London,  1881-1886,  Nos.  4,  p.  38;  5,  p.  59;  6,  p.  66;  7, 
p.  67;  8,  p.  67;  9,  p.  40. 


Bui.  32,  Hawaii  Agr.  Expt.  Station. 


Plate  I. 


Papaya  Orchard  in  which  Nearly  Every  Tree  is  Bearing  Fruit. 


Bui.  32,  Hawaii  Agr.  Expt.  Station. 


Plate  II, 


20a 


£5 


Bui.  32,  Hawaii  Agr.  Expt.  Station. 


Plate  III. 


Pistillate  Papaya  Tree  and  Flower  of  the  Dioecious  Type. 


Bui.  32,  Hawaii  Agr.  Expt.  Station. 


Plate  IV. 


Fig.  1.— Male  Papaya  Tree. 


Fig.  2.— Corre/e  Tree  with  a  Few  Fruits;  Staminate  Flowers  to  the  Right. 

One  flower  cut  open  exposing  stamens  and  rudimentary  pistil. 


17 

be  in  the  product  ion  of  a  more  carefully  prepared  product,  which 
would  replace  the  cheaper  and  adulterated  grades,  of  which  consid- 
erable quantities  are  Bold.  From  the  fact  that  the  prices  have  fallen 
in  recent  years  it  would  no!  seem  that  the  demand  is  very  brisk.  The 
Montserrat  industry  has  declined  to  souk*  extent. 

COLLECTING    AND    PREPARING    THE    JUI< 

There  are  no  difficulties  requiring  great  skill  in  collecting  and 
preparing  the  juice  for  market,  but  care  is  necessary.  Usually  only 
the  fruits  are  tapped.    These  abound  in  juice,  particularly  when  the 

tree  is  young  and  during  warm  weather  after  a  rain.  In  the  early 
morning  the  flow  is  most  abundant.  Very  shallow  incisions,  not  OTOT 
one-eighth  of  an  inch,  are  made  about  a  half  inch  apart,  lengthwise 
of  the  nearly  mature  green  fruits.  The  tapping  may  be  repeated 
several  times  at  intervals  of  three  or- four  days.  Only  nonmetallic 
instruments  should  be  used  in  tapping  or  in  collecting,  for  the  juice 
acts  upon  metals  and  becomes  discolored.  A  bone  or  ivory  blade 
may  be  used.  The  flow  i>  free  at  first  and  the  liquid  is  caught  in 
porcelain,  glass,  or  earthenware  Teasels.  Coagulation  soon  begins 
and  the  mass  must  be  scraped  from  the  surface  of  the  fruit.  In  most 
places  where  the  industry  is  conducted  labor  is  cheap,  but  it  would 
seem  that  a  more  convenient  and  efficient  vessel  could  be  devised 
winch  could  be  quickly  put  in  place  to  receive  the  juice,  permitting 
the  operator  to  proceed  to  the  next  tree 

The  juice  mibt  be  dried  promptly  after  it  is  collected  or  decompo- 
sition begins.  As  the  juice  Hows  most  freely  in  the  early  morning,  it 
is  usually  collected  then  and  dried  wholly  or  in  part  during  the  remain- 
der of  the  day.  Sun  drying  is  followed  to  some  extent,  but  artificial 
means,  such  as  are  furnished  by  a  fruit  drier  or  one  made  expressly 
for  the  purpose  are  preferred.  In  Montserrat  several  driers  have 
been  made  for  the  purpose  and  operated  by  the  companies  buying  the 
juice  from  the  peasants  who  gather  it.  One  form  of  drier  is  about 
3  by  3  feet,  and  0  feet  in  length.  The  sides  and  ends  are  of  brick  with 
an  opening  at  one  end  for  the  flue  and  at  the  other  end  to  admit  fuel 
The  top  is  open.  About  a  foot  below  the  top  a  sheet  of  iron  is  placed 
and  upon  this  an  inch  or  two  of  sand  to  modify  and  distribute  the  heal 
arising  from  the  lire  beneath.  The  coagulated  juice  is  spread  upon 
brown  linen  stretched  upon  frames  which  are  made  to  fit  the  top  of 
the  drier.  The  drying  must  be  effected  with  low  temperatures, 
trreat  heat  destroys  the  ferment.  A  temperature  below  100°  I  •  is 
preferred  by  some  operators.    The  coagulated  material  may   be 

placed  upon  of  glass  while  drying.     When  dry  and  flaky  it 

may  be  ground  in  a  coffee  mill,  preferably  while  warm,  and  should 


18 

then  be  in  the  form  of  a  white  or  cream-colored  powder,  which  should 
be  placed  in  bottles  and  tightly  closed. 

In  the  powdered  form  or  as  dried  flakes  it  is  exported  to  America 
and  Europe,  where  it  is  further  refined  and  sold  as  a  powder  or  in 
tablet  or  other  form,  under  various  tradenames  asupapoid,"  "caroid," 
"papain,"  "papayotin,"  etc. 

Little  information  is  available  as  to  yields.  Some  collectors  figure 
upon  a  yearly  production  of  1  pound  of  dried  latex  per  tree.  This 
is  probably  rather  a  high  estimate.  The  coagulated  latex  will  pro- 
duce about  25  per  cent  of  its  weight  in  dried  powder  which  still  con- 
tains from  6  to  10  per  cent  of  moisture.1  About  one-sixth  of  the 
dried  powder  is  papain. 

PART  II.  BREEDING  OF  PAPAYA. 

One  of  the  most  interesting  and  important  features  of  papaya 
study  is  breeding;  interesting  because  of  the  many  problems  which 
it  presents,  and  important  because  of  the  large  promise  of  improve- 
ment in  these  fruits.  This  part  of  the  paper  will  attempt  to  present 
descriptions  of  some  of  the  material  at  hand  for  such  work,  showing 
also  some  of  the  difficulties,  possibilities,  and  limitations  in  papaya 
breeding  so  far  as  they  have  appeared  in  the  work  performed  here. 

BOTANICAL  NAMES. 

Before  entering  upon  these  phases  of  the  subject  a  word  will  be 

in  order  as  to  the  names,  botanical  relationships,  and  distribution  of 

the  species.     Carica  papaya  Linn,  has  been  designated  botanically 

under  several  names  as  Carica  mamaja  Vellozo  (Fl.  Flumin.,  Vol. 

X,   t.    131);    Carica  Tiermaphrodita  Blanco   (Fl.   de  Filipinas,   Gran 

edicion  1879,  Vol.  Ill,  p.  212);  Papaya  vulgaris  A.  DC.   (Prodr., 

XV,  I,  p.  414);  and  Papaya  sativa  Lussac  (Fl.  des  Antilles,  Vol.  Ill, 

p.  45,  t.  10,  11). 

COMMON   NAMES. 

The  species  has  been  known  under  many  common  namjes,  as  tree 
melon,  melon  zapote,  pawpaw,  papaw,  lechoso,  maneo,  mamerio, 
papai,  papaya,  etc.  In  English-speaking  countries  the  name  papaya 
is  taking  the  place  of  tree  melon  and  pawpaw,  both  of  which  are 
misleading.  It  is  particularly  desirable  that  the  use  of  the  name 
papaw  to  designate  the  fruit  should  be  dropped,  since  its  application 
to  a  wholly  unrelated  species,  Asimina  triloba,  is  well  established. 
The  name  papaya,  which  now  should  be  adopted  generally,  is  believed 
to  be  of  Carib  origin,  and  is  heard  among  the  descendants  of  these 
aboriginal  peoples  in  various  forms,  as  "mapaya"  and  "mamaya," 

i  F.  B.  Kilmer.    The  Story  of  the  Papaw.    Amer.  Jour.  Pharm.,  73  (1901),  Nos.  6,  pp.  272-285;  7,  pp. 
336-348;  8,  pp.  383-395. 


being  supposed  by  Humboldt  to  be  a  derivative  of  "mapa,"  meaning 
honey.1 

BOTANICAL   RELATIONSHIPS. 

The  plants  of  the  genus  Caiica  have  been  referred  to  by  different 
botanists  to  the  families  Papayaceae,  Passifloreae,  and  Cucurbitaceae. 
This  and  the  genus  Jacaratia  now  constitute  the  family  Caricacese.2 
Carica  has  been  divided  into  the  three  subgenera  or  sections,  Vas- 
concellea,  Hemipapaya,  and  Eupapaya,  embracing  22  known  species, 
all  of  American  or  West  Indian  origin,  the  genus  being  represented 
from  Argentina  to  Mexico  and  in  the  Antilles.  Of  the  home  and 
probable  origin  of  C.  papaya,  mention  will  be  made  later. 

DESCRIPTIONS   OF   FORMS   OF   PAPAYA. 

The  above  will  serve  to  indicate  the  general  botanical  position  of  the 
papaya  and  its  relatives.  Breeding  at  this  station  has  been  confined 
chiefly  to  the  one  species  of  this  genus  C.  papaya,  C.  peltata,  and 
C.  quercifolio.  having  been  the  only  others  used.  Some  descriptions 
of  the  forms  in  which  the  papaya  itself  occurs  with  reference  chiefly 
to  the  distribution  of  the  sexes  and  the  shape  of  the  fruit  are  given 
below. 

Form  1.  The  first  form  to  be  considered  is  the  ordinary  female. 
Commonly  the  papaya  is  dioecious.  The  female  tree  produces  flowers 
exclusively  pistillate,  with  no  indication  of  even  the  remnants  of 
stamens  (PI.  Ill) .  At  first  sight  they  may  appear  to  be  polypetalous, 
since  the  corolla  tube  is  greatly  reduced,  but  closer  observation  re- 
veals their  gamopetalous  condition.  The  ovaries  and  the  resulting 
fruits  are  of  various  shapes,  inclining  to  the  obovoid,  with  a  diameter 
somewhat  shorter  than  the  major  axis,  and  the  surface  smooth  or  only 
slightly  ribbed.  The  fruits  are  usually  borne  singly  on  very  short 
peduncles  in  the  axils  of  the  leaves. 

Form  2.  The  male  tree  (PL  IV,  fig.  1),  the  counterpart  of  that  just 
referred  to,  produces  only  staminate  flowers  which,  however,  possess 
rudimentary  or  abortive  pistils  (PL  IV,  fig.  2),  and  hang  in  great  pro- 
fusion in  cymose  panicles  on  peduncles,  2  to  5  feet  in  length.  The 
flowers,  unlike  those  of  the  female  tree,  have  a  long  corolla  tube  in  the 
throat  of  which  are  10  stamens  arranged  in  two  series,  the  one  having 
slightly  longer  filaments  than  the  other.  At  the  base  of  the  tube 
may  be  found  a  small  rudimentary  pistil,  quite  devoid  of  any  stigma. 
Since  all  the  flowers  are  of  this  type  the  tree  abounds  in  pollen,  but 
produces  no  fruit.  In  foliage  and  habit,  other  than  as  described,  it 
resembles  the  female. 

i  Jour.  linn.  Soc.  [London],  Bot.,  10  (1809),  p.  14. 

>H.  Solms-Laubach.    Caricacee.    In  Martins,  Flora  Braailienais,  vol.  13,  pt.  3,  col.  171-190, 


20 

Form  3.  Correse  of  Solms-Laubach.  This  form  is  a  departure 
from  the  last  and  is  illustrated  in  Plate  IV,  figure  2.  It  is  identical 
with  the  tree  just  referred  to  except  that  a  few  of  its  flowers  have  pis- 
tils capable  of  fecundation.  The  rays  of  the  stigmas  may  be  per- 
fectly formed  or  one  or  more  may  be  aborted,  giving  rise  to  an  uns}^m- 
metrical  or  gibbous  fruit  in  which  the  corresponding  portions  of  the 
placenta  have  failed  to  develop.  The  ovaries  of  the  well-formed  her- 
maphrodite flowers  incline  more  to  the  elongated  and  cylindrical  form 
than  those  of  the  pistillate  tree  and  result  in  correspondingly  different 
fruits.  The  corolla  tube  is  elongated  as  in  the  staminate  flowers  and 
the  stamens  are  similarly  located  in  the  throat  of  the  corolla,  being 
brought  into  proximity  with  the  stigmas.  These  bisexual  flowers 
are  larger  than  the  staminate  but  in  other  respects  are  similar,  except 
as  has  just  been  indicated.  The  number  of  such  flowers  varies  from 
few  to  many  (PI.  V,  figs.  1  and  2),  there  being  at  times  as  many  form- 
ing fruits  on  the  long  pendulous  peduncles  as  are  to  be  found  on  some 
pistillate  trees,  notwithstanding  the  fact  that  many  have  fallen. 
Often  as  the  fruit  develops  the  peduncle  is  not  strong  enough  to  sus- 
tain the  weight  and  breaks  off,  such  long  fruit  stems  being  poorly 
adapted  to  their  work  of  supporting  the  fruit  and  inviting  disaster 
from  the  winds. 

What  causes  may  have  given  rise  to  the  formation  of  bisexual  flow- 
ers on  these  otherwise  male  trees  and  to  what  extent  such  plants  may 
be  regarded  as  varietal  in  their  rank  may  be  referred  to  later.  Here 
it  is  intended  merely  to  point  out  that  such  forms  exist  and  to  indi- 
cate their  character.  This  form  of  andromonoecious  *  papaya  was 
described  by  Correa  de  Mello  and  Spruce,2  and  in  honor  of  the  former 
has  been  named  by  Solms-Laubach  3  form  correa?. 

Attention  has  just  been  called  to  the  variations  in  the  number  of 
fruits  produced  by  this  form  correse.  It  may  also  be  pointed  out  that 
there  are  many  gradations  in  the  length  of  the  peduncles. 

Form  4.  Elongata,  a  hermaphrodite  papaya  (PI.  VI).  This  tree 
produces  two  types  of  flowers.  One  of  these  types  is  hermaphrodite 
and  is  in  every  way  similar  to  a  well-formed  bisexual  flower  on  the 
correas  form  (form  3),  except  that  it  usually  is  larger  and  its  pistil  is 
more  elongated  ( PI.  VII,  fig.  1) .  The  other  type  of  flower  is  staminate 
and  is  identical  in  appearance  with  the  staminate  flowers  already  de- 
scribed. Because  of  the  presence  of  these  two  types  of  flowers,  this 
form  has  been  referred  to  in  the  earlier  publications  of  this  station 
as  the  monoecious  papaya.4 

1  Having  both  staminate  and  hermaphrodite  flowers  on  the  same  plant. 

*  Jour.  Linn.  Soc.  [London],  Bot.,  10  (1869),  p.  3. 

a  Die  Heimath  und  der  Ursprung  des  cultivirten  Melonenbaumes,  Carica  papaya.    Bot.  Ztg.,  47  (1889), 
Nos.  44-49. 

♦  Hawaii  Sta.  Rpts.  1910, 1911,  and  1912. 


21 

As  experiments  have  proceeded,  however,  it  has  been  discovered 
that  the  pollen  from  such  staminate  flowers,  except  in  the  case  of  one 
tree,  failed  to  fecundate  any  pistils  up  to  the  present  time,  and  it  has 
boon  applied  to  every  type  of  pistil  found  in  the  station  collection. 
Since  these  flowers  apparently  do  not  function  it  seems  incorrect  at 
present  to  apply  to  this  form  of  the  papaya  the  term  monoecious. 
They  may  rather  be  termed  either  pseudomonoecious  or  hermaphro- 
dite. These  remarks  anticipate,  to  some  extent,  facts  which  will  be 
brought  out  later,  but  are  made  here  as  an  explanation  of  the  change 
in  terminology. 

To  proceed  further  with  the  description  of  this  form,  it  is  to  be 
noted  that  the  two  types  of  flowers  are  found  in  the  same  cluster,  as 
was  true  in  the  last  form  described,  but  in  the  present  case  the  inflores- 
cence is  much  shortened,  being  generally  from  3  inches  to  6  inches  long. 
After  the  tree  attains  sufficient  maturity  a  flower  cluster  is  usually 
formed  in  the  axil  of  each  leaf,  but  on  some  trees  many  of  these 
clusters  produce  only  the  staminate  flowers.  Not  infrequently  2 
feet  or  more  of  the  trunk  may  yield  no  hermaphrodite  flowers  and 
consequently  no  fruit,  leaving  that  portion  of  the  trunk  bare  after 
the  flowers  have  fallen  (PL  VII,  fig.  1).  There  may  be  one  or  several 
bisexual  flowers  in  each  cluster,  resulting  in  fruit.  The  fruit  from 
this  hermaphrodite  flower  inclines  to  be  elongated,  cylindrical,  and 
pointed  at  the  outer  end,  but  the  shape  varies  as  in  all  papayas. 
The  form  which  Correa  de  Mello  and  Spruce  mention  as  "Chamburu" 1 
and  which  they  found  in  the  equatorial  Andes,  appears  to  be  very 
similar  to  this  and  may  perhaps  be  identical. 

Form  5.  Sterile  hermaphrodite.  This  may  be  regarded  as  an 
extreme  case  of  unproductiveness  of  the  form  just  described.  It  has 
been  represented  by  only  one  tree,  so  far  as  known.  This  has  pro- 
duced no  fruit.  A  few  hermaphrodite  flowers  were  found,  but  none 
matured  fruit  (PL  VII,  fig.  2).  The  pollen  of  staminate  flowers  was 
unfertile. 

Form  6.  Forbesii  of  Solms-Laubach.  Forbes 2  describes  a  ceeno- 
monoecious 3  form  which  he  found  at  Bantam,  Java,  and  which 
resembles,  yet  is  quite  different  from,  the  form  correse  described 
above  (form  3) .  Solms-Laubach  later  described  the  same  form 4 
which  he  found  in  another  part  of  the  same  island.  To  this  he  applied 
the  name  forbesii.  Briefly  stated,  the  most  striking  characters  of 
this  plant  are  as  follows:  On  the  long,  pendulous  peduncles,  charac- 
teristic of  the  male  tree,  this  plant  produces  its  three  types  of  flowers, 
staminate,  pistillate,  and  hermaphrodite.     The  staminate  are  identical 

i  Jour.  Linn.  Soc.  [London],  Bot.,  10  (1869),  p.  11. 

*  H.  O.  Forbes.    Jour.  Bot.  [London],  n.  ser.,  8  (1879),  p.  313. 

»  Having  male,  female,  and  hermaphrodite  flowers  on  the  same  plant. 

*  Bot.  Ztg.,loc.  cit. 


22 

with  those  of  the  ordinary  male  tree  and  the  pistillate  with  those  of 
the  female  tree,  but  the  hermaphrodite  differ  from  those  described 
above  (form  3) .  These  have  a  very  much  shortened  corolla  tube,  as 
in  the  case  of  the  pistillate  flower,  the  lobes  being  divided  almost  to 
the  base  of  the  ovary.  On  the  edge  of  this  short  tube,  quite  near  the 
base  of  the  ovary,  are  attached  only  five  stamens,  and  these  are  sup- 
plied with  long  filaments,  which  rest  in  furrows  between  the  lobes 
of  the  ovary.  These  lobes  are  united  at  the  base,  but  often  separable 
at  the  upper  ends.     The  resulting  fruit  is  deeply  furrowed. 

This  form  of  the  papaya  has  not  been  seen  in  Hawaii  by  the  writers, 
although  thousands  of  plants  have  been  under  observation  at  the 
experiment  station  and  in  other  parts  of  the  islands.  This  is  rather 
remarkable  when  it  is  remembered  that  the  next  form  closely  resem- 
bling it  is  not  at  all  rare  in  Hawaii. 

Form  7.  Pentandria.  This  form  produces  hermaphrodite  flowers 
of  the  same  type  as  those  just  described  (form  6).  They  have  the 
corolla  tube  reduced  to  almost  negligible  length  and  the  5  stamens 
inserted  on  long  filaments  on  this  tube,  near  the  base  of  the  ovary 
(PI.  VIII,  inset).  The  ovary  is  deeply  furrowed,  with  the  stamens 
lying  in  the  grooves  between  the  lobes,  thus  giving  rise  to  a  deeply 
furrowed  fruit.  There  are  also  staminate  flowers  of  the  ordinary 
type,  and  these  are  born  with  the  hermaphrodite  in  short  clusters  as 
in  the  case  of  form  4. 

Form  8.  This  is  the  coexistence  of  the  forms  4  arid  7  in  the  same 
plant  (PL  VIII).  The  staminate  flowers  of  the  cluster  are  the  same 
as  in  all  cases,  but  the  two  forms  of  hermaphrodite  flowers  occur  side 
by  side  in  the  same  plant  and  give  rise  to  correspondingly  different 
fruits. 

Form  9.  Intermediates.  Here,  in  still  other  monoecious  or  her- 
maphrodite plants,  are  to  be  found  almost  all  possible  combinations 
of  the  characters  of  hermaphrodite  flowers  of  the  forms  4  and  7 
(PL  IX,  fig.  1).  The  corolla  may  be  intermediate  in  form  between 
the  long  tube  and  the  short.  The  stamens  may  be  long,  short,  or 
intermediate,  and  may  be  attached  at  any  one  of  several  points  on 
the  corolla  or  even  on  the  lobes  of  the  ovary.  The  stamens  may  be 
from  Hve  to  ten  in  number.  The  ovary  is  often  misshapen,  the  lobes 
being  only  partly  united,  resulting  in  a  distorted  fruit.  Occasionally 
a  flower  may  be  of  the  form  4  on  one  side  and  of  the  form  7  on  the 
other. 

Form  10.  A  curious  andromonoecious  form  has  recently  been 
observed  at  this  station.  Many  hermaphrodite  flowers  of  various 
characters,  as  described  above,  are  found  on  the  plant,  but  the  most 
curious  character  is  the  bearing  of  ovules  on  the  stamens  of  some  of 
these  hermaphrodite  flowers.     With  respect  to  its  long  peduncles 


23 

and  in  general  appearance  this  form  is  the  same  as  the  male  or  the 
hermaphroditic  males  forbesii  and  correaB. 

Form  1 1 .  Ernstii  of  Solms-Laubach.  From  the  description  given 
by  Ernst 1  this  appears  to  represent  the  coexistence  on  'the  same 
tree  of  pistillate  flowers  and  of  hermaphrodite  flowers  of  the  same 
characters  as  those  of  form  4.  No  staminate  flowers  were  found  by 
Ernst  on  such  trees.  He  states:  "Papaya  has  three  different  kinds 
of  flowers — staminiferous,  pistilliferous,  and  hermaphrodite.  The 
latter  two  are  found  on  the  same  tree,  whereas  the  stamen-bearing 
flowers  grow  exclusively  on  distinct  individuals."  He  found  her- 
maphrodite flowers  "on  all  the  female  trees  examined,  though  never 
in  great  numbers."  In  his  description  these  hermaphrodite  flowers 
are  stated  to  be  gamopetalous  (in  contradistinction  to  the  pistillate, 
which  he  regarded  as  polypetalous)  and  to  possess  an  ovoid  corolla 
tube  in  the  throat  of  which  the  stamens  are  inserted.  This  distribu- 
tion of  the  sexes  has  not  been  noted  in  Hawaii. 

Form  12.  A  tree  similar  to  the  above  but  bearing  staminate 
flowers  as  well  as  pistillate  and  hermaphrodite  was  seen  by  one  of  the 
writers  a  few  years  ago  at  this  station.  Whether  the  pollen  from  the 
staminate  flowers  was  incapable  of  fecundating  any  pistil  was  not 
determined. 

Form  13.  Pistillate  and  staminate  flowers  on  the  same  tree. 
Recorded  by  Iorns  (see  p.  25). 

SUMMARY   OF   FORMS. 

To  summarize  briefly,  there  may  be  said  to  be  the  following  forms : 

1.  The  female  of  the  dioecious  papaya. 

2.  The  male  of  the  dioecious  papaya. 

3.  The  correae  form  of  andromoncecious  papaya,  with  its  elongated 
corolla  tube  and  10  stamens  in  the  throat;  flower  clusters  and  other 
characters  like  male. 

4.  The  elongata  form  with  its  hermaphrodite  flowers  like  those  of 
correae  and  its  staminate  flowers  nonfunctioning;  flower  clusters 
short;  fruits  elongated,  tending  to  cylindrical  shape. 

5.  The  sterile  hermaphrodite,  similar  to  4,  but  without  fruits. 

6.  The  forbesii  form  of  andromoncecious  papaya,  with  its  stamens 
in  the  hermaphrodite  flower  reduced  to  five  in  number,  and  these 
attached  by  long  filaments  to  the  shortened  corolla  tube  near  the 
base  of  the  ovary;  flower  clusters  and  other  characters  like  male. 

7.  The  pentandria  form  with  its  hermaphrodite  flowers  like  those 
of  forbesii,  staminate  flowers  nonfunctioning;  flower  clusters  short; 
fruit  generally  club-shaped  or  obovate  and  furrowed. 

8.  The  coexistence  of  forms  4  and  7  in  the  same  plant. 

i  A.  Ernst.    Jour.  Hot.  [I.ond.n],  4  (1866), pp.  81-83. 


24 


9.  Intermediates   combining   in   various   ways   the   characters   of 
forms  4  and  7. 

10.  Andromonoecious  with  misplaced  ovules. 

11.  Ernstii.     Pistillate  and  hermaphrodite  flowers  on  the  same 
tree,  but  no  staminate  flowers. 

12.  Pistillate,  hermaphrodite,  and  staminate  flowers,  with  short 
peduncles,  on  the  same  tree. 

13.  Pistillate  and  staminate  flowers  on  the  same  tree. 
Disregarding  the  nonfunctioning  staminate  flowers  of  most  elongata, 

it  will  be  seen  that  there  are  represented  all  the  possible  combinations 
of  staminate,  pistillate,  and  hermaphrodite  flowers  and  individuals. 
Kepresenting  the  three  elements  by  a,  b,  and  c,  the  seven  possible 
distributions  would  be  as  follows :  a,  b,  c,  ab,  ac,  be,  and  abc.  Repre- 
sented diagramatically  with  the  usual  signs  these  would  be  as  indi- 
cated below: 


s 

/ 

?\ 

/* 

?\ 

s 

/ 

3 
/ 

H 

\ 


/ 


ab 


ac 


be 


abc 


a  is  represented  by  form  2. 

b  is  represented  by  form  1,  also  in  most  of  the  progeny  of  stocks  of 
forms  3,  4,  6,  7,  and  perhaps  others. 
c  is  represented  by  forms  4,  7,  8,  9. 
ab  is  represented  by  form  13. 
ac  is  represented  by  forms  3,  6. 
be  is  represented  by  form  11. 

abc  is  represented  by  form  12  and  occasionally  by  forms  3  and  6. 
Seeds  of  form  1  will  produce  a  population  whose  formula  may  be 

written  thus:     9^|  \/S 

The  stocks  of  forms  3  and  6,  expressed  in  formula  may  be: 


\ 


( 


occasional 


) 


The  formula  for  stocks  of  forms  4,  7,  8  and  9  would  be. 


\ 


( 


^occasional  ). 


Seeds  of  forms  11  and  12  have  not  been  planted  and  the  formulas 
for  the  progeny  can  not  be  stated. 


Bui.  32,  Hawaii  Agr.  Expt.  Station. 


Plate  V. 


Elonqata  Tree  and  Fruit. 


Bui.  32,  Hawaii  Agr.  Expt.  Station. 


Plate  VII. 


Fig.  1.— Elongata  Tree  With  Long  Bare  Spaces,  and  Elongata  Hermaphrodite 

Flower. 


Fig.  2.— Sterile  Hermaphrodite  Tree. 


Bui.  32,  Hawaii  Agr.  Expt.  Station. 


Plate  VIII. 


Elonqata  and  Pentandria  Fruits  on  the  Same  Tree,   Pentandria  Flowers, 
and  a  Fruit  Within  a  Fruit. 


Bui.  32,  Hawaii  Agr.  Expt.  Station. 


Plate  IX. 


Fig.  1  .—Intermediate  Forms. 


Fig.  2.— An  Example  of  Parthenocarpic  Development. 


Bui.  32,  Hawaii  Agr.  Expt.  Station. 


Plate  X. 


25 

SIGNIFICANCE    OF  THE    FORMS. 

It  will  be  seen  at  once  that  many  of  these  "forms"  are  merely  an 
expression  of  the  different  manner  of  the  distribution  of  the  sexes, 
hut  some  are  distinct  and  have  a  very  practical  bearing  upon  the 
subject  of  breeding.  Perhaps  the  most  important  are  the  male  and 
female  of  the  dioecious  papaya,  by  far  the  most  common,  and  to  many 
the  only  familiar  papaya;  the  two  andromonoecious  forms,  correae 
and  forbesii:  and  the  two  hermaphrodite  forms,  elongata  and  pen- 
tandria.  There  are  mentioned  in  the  above  list  of  twelve  forms  and 
methods  of  distribution  of  the  sexes  only  those  wThich  have  been  seen 
hi  Hawaii,  and  two  other  forms,  forbesii,  which  have  been  so  fully 
reported  upon  by  Forbes  and  by  Solms-Laubach,  and  ernstii,  by 

Ernst. 

CHANGE    OF    SEX. 

It  is  a  fact  worthy  of  note  that  some  of  these  forms  are  not  con- 
stant. One  may  assume  the  r61e  of  another.  Perhaps  the  most 
primary  change  of  sex  which  takes  place  is  to  be  observed  in  the 
appearance  of  hermaphrodite  flowers  on  trees  that  have  previously 
produced  only  staminate  inflorescence.  That  is,  form  2  may  pass 
into  form  3  or  form  6.  Not  only  is  it  known  that  such  changes  take 
place,  but  the  conditions  which  may  bring  them  about  have  been 
under  observation.  This  " fruiting  of  the  male  papaya"  takes  place 
most  freely  in  cool  climates  outside  the  Tropics  or  at  high  altitudes. 
In  Hawaii  it  may  be  seen  that  these  trees  fruit  more  abundantly  on 
the  mountains  than  near  the  sea  level.  Information  received  by 
correspondence  with  experiment  stations  and  botanic  gardens  in 
many  parts  of  the  world,  in  reply  to  direct  inquiry,  have  confirmed 
this  conclusion.  In  torrid  climates  the  fruiting  of  the  male  is  rare. 
It  is  to  be  remembered  in  this  connection  that  all  the  staminate 
flowers  of  the  male  trees  possess  an  undeveloped  or  an  abortive  pistil. 
The  only  change  in  the  cases  mentioned  consists  in  the  development 
of  this  pistil. 

The  late  M.  J.  Iorns  '  reported  the  appearance  of  female  flowers 
on  male  trees  as  a  result  of  the  removal  of  the  terminal  bud.  In  the 
popular  literature  of  the  papaya  there  are  many  references  to  the 
acquiring  of  fruit-bearing  habits  by  the  male  tree,  due  supposedly 
to  some  injury,  such  as  the  removal  of  the  terminal  bud  or  the  break- 
ing of  the  roots  in  transplanting  old  male  trees.  It  is  an  interesting 
and  ive  fact  that  none  of  these  methods  of  treatment  bring 

about  the  results  unfailingly,  and  there  appear  to  be  other  conditions 
entering  into  the  problem.  Iorns  undertook  his  experiments  in  part 
to  disprove  an  idea  prevalent  among  the  native  Porto  Ricans  to  the 

»  Science,  n.  ser.,28  (1908),  No  .,126. 


26 

effect  that  this  change  would  be  brought  about  if  the  terminal  bud 
be  removed  during  a  certain  phase  of  the  moon.  Some  of  his  trees 
so  treated  showed  the  change  but  others  did  not.  Those  treated  at 
fairly  definitely  recurring  periods,  however,  were  the  specimens 
which  appeared  to  undergo  the  change.  He  reached  the  conclusion 
that  other  conditions  than  the  loss  of  the  terminal  bud  must  be  pres- 
ent, and  suggested  that  the  trees  may  pass  through  cycles  of  develop- 
ment and  be  subject  to  this  change  only  at  certain  times.  It  is  a  well- 
known  fact  that  merely  removing  the  terminal  bud  can  not  be 
depended  upon  to  produce  the  change. 

The  complete  change  of  a  male  tree  to  one  purely  female,  with  fruits 
of  the  form  of  the  ordinary  dioecious  papaya,  is  perhaps  the  most 
remarkable.  A  well  authenticated  case  of  this  character  has  been 
reported  to  the  writers  and  the  tree  in  its  present  condition  has  been 
examined.  This  tree,  which  is  represented  in  Plate  X,  figure  1,  pro- 
duces pistillate  flowers.  When  examined  and  photographed  on  Janu- 
ary 24,  1913,  no  evidence  could  be  found  of  any  staminate  or  hermaph- 
rodite flowers,  or  of  any  fruits  which  appeared  to  have  grown  from 
the  latter.  All  the  branches  were  producing  fruit,  except  one  which 
was  too  small  and  weak,  being  crowded  out  by  the  larger  members. 
Dr.  John  T.  Gulick,  a  scientist  of  wide  reputation,  whose  studies  in  evo- 
lution published  by  the  Carnegie  Institution  would  alone  be  sufficient 
to  establish  his  accuracy  of  observation  and  statement,  has  kindly 
furnished  this  station  with  the  history  of  this  tree,* which  has  grown 
in  his  garden.     His  letter  reads  as  follows : 

Honolulu,  May  28,  1913. 
J.  E.  Higgins,  Esq. 

Dear  Sir:  In  reply  to  your  request  for  the  history  of  the  papaya  tree  that  changed 
its  habits  after  being  beheaded,  I  am  able  to  give  a  few  facts. 

When  the  tree  was  a  year  and  a  half  or  two  years  old  it  had  produced  only  staminate 
flowers,  growing  on  long,  dangling  branches.  It  was  then  6  or  7  feet  high,  and  as  the 
only  use  we  had  for  it  was  as  a  support  for  a  clothesline,  we  cut  off  the  leaves  and  the 
top  of  the  tree  that  were  in  the  way  of  the  hanging  clothes. 

It  was  not  till  many  months  later  that  we  noticed  that  the  new  branches  were  bearing 
fruit  and  that  the  flowers  were  all  pistillate.  During  the  three  years  that  have  passed 
since  its  head  was  cut  off  it  has  developed  10  branches,  some  of  them  being  8  or  9  feet 
in  length,  and  all  of  them  producing  pistillate  flowers  and  fruit.  The  trunk  has  also 
grown  in  size  till  now  about  18  inches  in  diameter. 
Yours,  truly, 

(Signed)  John  T.  Gulick. 

It  will  be  seen  from  the  above  that  no  known  factor  has  entered  as 
a  cause  of  this  change  except  the  removal  of  the  whole  top  of  the  tree. 
Why  so  marked  a  result  should  follow  such  treatment  in  this  case, 
while  in  many  others  no  change  is  brought  about  in  the  character  of 
the  flowers,  is  a  question  wholly  unsettled.  The  theory  of  cyclic 
development  proposed  by  Iorns  offers  a  possible  hypothesis.     The 


27 

question  may  then  be  raised  as  to  whether  this  potentiality  to  change 
exists  in  all  parts  of  the  plant  at  the  supposed  seasons  of  susceptibility 
or  whether  these  stages  of  development  are  registered  in  the  different 
parts  of  the  plant  as  they  are  developed,  in  a  manner  like  bud  varia- 
tions. Nearly  all  the  buds  in  the  upper  part  of  the  papaya  tree, 
except  the  terminal,  remain  dormant  unless  some  injury  occurs  to 
the  latter.  If  these  possibilities  to  change  exist  as  bud  variations 
and  it  be  necessary  only  to  force  the  buds  into  growth  in  order  to 
bring  the  differences  into  evidence,  then  it  would  follow  that,  while 
the  removal  of  the  terminal  bud  at  different  seasons  might  produce 
results,  or  not,  according  to  the  character  of  the  buds  immediately 
below,  the  cutting  at  some  point  lower  down  might  bring  about  the 
change.  An  explanation  of  these  phenomena  on  the  basis  of  bud 
variation,  however,  need  not  presuppose  a  cyclic  development  or  the 
possibility  of  changing  all  male  trees.  There  is  no  lack  of  evidence 
that  some  of  the  unit  characters  of  a  hybrid  may  become  separated  in 
different  parts  of  the  plant.  A  hibiscus  hybrid  in  the  experiment 
gardens  of  this  station  produces  flowers  of  different  form  and  coloring 
on  each  of  several  main  branches.  It  is  well  known  that  peach  trees 
occasionally  produce  nectarines.  But  it  is  not  necessary  here  to 
multiply  instances  of  bud  variation  of  which  probably  no  better 
explanation  has  been  offered  than  that  they  represent  a  character  of 
some  antecedent.  Whether  the  facts  of  changing  sex  as  presented 
are  to  be  explained  on  a  bud  variation  hypothesis  is  a  matter  of  specu- 
lation, but  the  suggestion  is  made  as  one  perhaps  worthy  of  consid- 
eration in  seeking  a  cause  of  the  known  facts. 

Whatever  theories  may  be  entertained  as  to  the  causes  of  the  phe- 
nomena of  changing  sex,  it  still  must  be  admitted  that  no  practical 
and  reliable  method  is  at  present  available  for  converting  a  male  tree 
to  one  bearing  fruit. 

THE  FEMALE  IN  SEX  CHANGE. 

It  is  worthy  of  note  that  no  record  has  been  found  by  the  writers, 
in  the  literature  of  the  papaya,  which  would  indicate  that  the  female 
or  pistillate  tree  has  ever  changed  its  sex.  There  are  numerous 
reports  of  so-called  "female"  trees  bearing  hermaphrodite  flowers  or 
staminate,  but  this  is  apparently  an  inaccuracy  in  language,  since  in 
such  cases  no  statement  is  made  that  a  tree  once  purely  pistillate  in 
character  has  changed  to  one  bearing  other  kinds  of  flowers.  As  has 
already  been  pointed  out,  there  are  forms  with  pistillate  and  other 
flowers  mixed,  and  these  have  often  been  termed  in  a  general  but 
incorrect  way  ''female  trees/'  but  such,  so  far  as  the  records  show,, 
have  been  the  same  in  character  throughout  their  existence. 


28 

INHERITANCE    OF   CHANGE    OF   SEX. 

Some  of  these  changes  in  sex,  when  they  have  been  brought  about, 
tend  to  reproduce  themselves  in  the  offspring  of  such  plants.  It  has 
been  shown  that  climatic  or  other  conditions  may  cause  male  trees 
to  change  the  character  of  many  of  their  flowers  to  hermaphrodite. 
In  the  station  experiment  orchards,  where  seeds  of  papaya  from  many 
sources  have  been  planted,  it  has  been  very  apparent  that  certain 
lots  show  a  much  stronger  tendency  to  produce  hermaphrodite  flowers 
than  others  growing  under  the  same  conditions.  For  example,  seeds 
of  a  papaya  from  South  Africa  were  received  through  the  Office  of 
Seed  and  Plant  Introduction,  of  the  United  States  Department  of 
Agriculture.    These  were  from  Singerton,  near  Hectorspruit,  Transvaal.1 

Prof.  J.  Burtt  Davy,  who  presented  them,  states  that  "these  seeds 
were  procured  at  an  altitude  of  1,200  feet,  subtropical  climate,  and 
rather  dry.,,  The  progeny  (Hawaii  Station  No.  1996)  was  33  pis- 
tillate trees  and  27  males  and  hermaphroditic  males,  several  exhibit- 
ing a  tendency  to  hermaphroditism  and  bearing  fruits.  Seeds  from 
one  of  the  trees  showing  the  tendency  in  a  high  degree  were  planted 
as  No.  2599.  Of  the  16  trees  set  in  the  orchard  4  were  pistillate,  3 
males,  and  9  hermaphroditic  males.  Of  the  latter,  one  carried  at  the 
time  of  counting  21  fruits,  another  37,  and  still  another  87.  Near 
these  were  other  papaya  trees,  growing  under  similar  conditions,  but 
presenting  only  pure  pistillate  and  pure  staminate  specimens.  It 
would  appear,  therefore,  that  such  alterations  in  sex,  once  established, 
tend  to  persist  under  conditions  different  from  those  in  which  they 
arose. 

ORIGIN   OF   DIFFERENT   FORMS. 

Having  in  mind  the  facts  as  outlined  above,  some  discussion  may 
be  undertaken  as  to  the  probable  origin  of  some  of  the  different  forms 
and  manner  of  sex  distribution,  to  which  reference  has  been  made. 

Form  3,  correse,  has  been  referred  to  as  a  modification  of  form  2, 
whereby  the  aborted  pistil  becomes  developed.  It  is  but  a  slight 
modification,  because  the  ovary  is  nearly  always  present  in  the  ordi- 
nary male. 

Form  4,  elongata.  Although  this  form  is  so  distinct  from  a 
practical  point  of  view,  and  to  casual  observation  so  different  from 
any  other,  it  will  be  seen  that  it  differs  from  form  3,  correae,  only  in 
three  minor  particulars:  (a)  Its  flower  clusters  are  greatly  shortened; 
(b)  it  produces  larger  fruits  than  the  average  correae;  and  (c)  its 
staminate  flowers  do  not  produce  fertile  pollen. 

In  the  matter  of  the  peduncle  it  may  be  said  that  practically  all 
degrees  of  length  have  been  observed  here,  from  the  very  long  to 

i  S.  P.  I.  No.  23915.    U.  S.  Dept.  Agr.,  Bur.  Plant  Indus.  Bui.  153,  p.  XI. 


29 

those  about  a  foot  in  length,  so  that  it  would  be  difficult  to  determine 
whether  to  class  the  specimens  as  correae  or  elongata.  That  the 
elongate  fruits  are  generally  larger  need  give  us  no  concern,  particu- 
larly because  correae  sometimes  bears  a  fruit  as  large  as  the  average 
elongata.  The  fact  that  the  staminate  flowers  of  elongata  have  not 
usually  been  found  to  produce  fertile  pollen  appears  to  furnish  some 
evidence  that  the  evolution  has  been  from  correae  to  elongata,  and 
not  the  reverse.  This  may  be  an  atavistic  development  toward  some 
hermaphroditic  antecedent  from  which  the  dioecious  papaya  has  been 
derived.  It  has  been  mentioned  that  cold  climate  increases  fructi- 
fication of  the  male  tree. 

In  this  connection  it  will  be  interesting  to  note  a  form  observed  by 
Correa  de  Mello  and  Spruce,1  and  spoken  of  by  them  as  "the  common 
Carica  of  the  equatorial  Andes,  where  it  is  cultivated  up  to  9,000  feet 
for  the  sake  of  its  edible  fruit."  It  is  there  known  as  "Chamburu." 
The  fruits  are  described  as  "  8  or  9  inches  long  and  sometimes  nearly 
as  broad.  The  flesh  is  whitish  (not  yellow,  as  in  the  papaw),  soft, 
and  with  a  pleasant  flavor — in  cool  sites  sometimes  very  acid/' 
Andre  2  states  that  while  traveling  in  the  Andes  of  Ecuador,  near  the 
Colombian  frontier,  he  found  two  varieties  of  papaya  which  were 
growing  in  cool  territory,  and  which  he  cites  as  examples  of  the  fact 
that  "certain  varieties  of  papaya  are  more  hardy  than  others. " 
'•  Two  small  trees,"  he  continues,  "struck  my  attention  in  this  pretty 
garden.  These  two  varieties  I  have  not  seen  anywhere  else.  The 
one  has  an  oblong  fruit,  very  beautiful,  cylindrical,  mucronate,  named 
ChamburoT  There  can  be  very  little  doubt  that  "Chamburu"  of 
Correa  de  Mello  and  Spruce,  and  "Chamburo"  of  Andre,  are  identical. 
Anyone  familiar  with  the  form  to  which  the  name  elongata  has  been 
applied  in  this  bulletin  will  be  impressed  at  once  with  its  similarity 
with  Chamburu  or  Chamburo  in  practically  every  particular  in  which 
the  latter  is  described.  The  similarity  is  so  strong  as  to  suggest  one 
of  two  explanations,  viz,  identity,  or  that  Chamburu  represents,  in 
the  evolution  of  the  papaya,  an  early  form  toward  which  elongata  is 
an  atavism.  Correa  de  Mello  and  Spruce  state  that  they  are  unable 
to  identify  this  with  any  described  species,  a  fact  which  is  not  remark- 
able, if  it  be  the  same  as  elongata,  since  Carica  "papaya  has  always  been 
described  from  its  dioecious  or  its  andromoncecious  forms.  In  their 
descriptions  of  forms  of  the  papaya  and  other  species  of  Carica,  no 
other  form  can  be  found  which  corresponds  to  elongata.  Elongata 
has  the  appearance  of  having  been  derived  from  the  male  through 
correae  by  an  increase  in  the  number  of  hermaphrodite  flowers  and 
a  shortening  of  the  peduncles,  a  process  which  takes  place  in  cool 
climates.  It  is  in  this  connection  also  that  its  possible  relation  to 
Chamburu  of  the  highlands  would  be  pointed  out. 

I  Jour.  Linn.  Soc.  [London],  Bot.,  10  (1869),  p.  11.  »  Rev.  Hort.  [Paris],  76  (1904),  p.  543. 


30 

Elongata  is  now  quite  widely  distributed,  but  has  received  very 
little  attention.  In  many  parts  of  the  East  it  is  known  as  the  "Ceylon 
papaya"  or  the  "Ceylon  Long,"  the  seed  having  been  distributed 
from  that  center.  It  is  believed  to  have  been  sent  to  Hawaii  from 
Ceylon  by  Prof.  A.  Koebele  about  the  year  1896. 

To  one  seeking  for  a  monoecious  or  hermaphroditic  ancestry  for 
the  common  papaya,  the  idea  may  suggest  itself  that  the  evolution 
has  been  from  elongata  through  correse  to  the  pure  staminate,  but 
on  such  a  hypothesis  it  is  difficult  to  account  for  the  nonfunctioning 
staminate  flowers  of  elongata,  while  those  of  correse  are  so  active. 
Further,  if  elongata  were  the  more  primitive  type,  it  is  to  be  pre- 
sumed that  it  would  have  become  more  generally  distributed  at 
very  early  times  and  would  have  attracted  the  attention  of  botanists 
who,  as  has  been  shown,  have  scarcely  mentioned  it,  while  correse 
and  the  strictly  dioecious  form  of  papaya  have  been  described  in 
detail. 

Form  5.  The  sterile  hermaphrodite  is  merely  the  extreme  of 
barrenness  in  form  4. 

Form  10.  The  andromonoecious  form  with  the  misplaced  ovules. 
This  is  a  peculiar,  but  significant,  arrangement  of  sex  organs.  It 
will  be  recalled  (see  p.  22)  that  the  peculiarity  of  the  form  is  in  its 
occasionally  producing  ovules  on  the  stamens  of  its  hermaphrodite 
flowers.  There  can  be  no  doubt  that  it  has  been  derived  from  the 
ordinary  male  tree,  but  its  peculiar  significance  lies  in  the  tendency 
which  it  shows  to  convert  some  of  its  stamens  into  carpels,  and, 
therefore,  in  the  light  which  it  throws  upon  the  peculiarities  of  the 
form  6. 

Form  6,  forbesii.  Here  the  process  has  gone  on  so  far  that  the 
ten  stamens  of  the  ordinary  male  have  been  reduced  to  five,  the  inner 
five  apparently  having  been  changed  to  carpels.  There  are  several 
indications  of  this,  (a)  The  fruit  is  very  deeply  furrowed,  often 
showing  the  newly  formed  carpels  quite  separated  from  each  other  at 
the  top,  and  for  a  considerable  distance  toward  the  base,  (b)  An- 
thers are  often  found  upon  the  carpels,  (c)  Occasionally  within  a 
fruit  formed  of  such  carpels  a  body  resembling  another  papaya 
fruit  is  to  be  found  (PI.  VIII,  inset),  which  may  be  regarded  as  the 
original  ovary  which  in  the  ordinary  forbesii  has  been  eliminated, 
(d)  One  of  these  irregular  and  partly  separated  carpels  is  some- 
times rolled  within  the  others,  giving  an  effect  somewhat  similar 
to  the  one  just  cited. 

It  appears  probable  that  forbesii  as  found  to-day  has  been  developed 
from  the  ordinary  male  form,  through  a  process  hinted  at  in  form 
10,  and  by  conditions  similar  to  those  which  are  believed  to  have 
produced  correae.  Why  the  evolution  should  take  place  along 
these  two  different  lines  is  an  interesting  question. 


31 

Form  7,  pentandria.  It  will  be  observed  from  the  description 
that  this  differs  from  forbesii  in  only  two  particulars,  (a)  The 
flower  clusters  of  pentandria  are  short  as  in  elongata,  while  those  of 
forbesii  are  long.  This,  as  has  been  indicated,  is  a  very  minor 
difference,  (b)  Pentandria  in  its  purest  state  produces  no  pistillate 
flowers.  However,  it  is  highly  probable  that  there  are  specimens 
of  forbesii  which  produce  only  staminate  and  hermaphrodite  flowers. 

It  naturally  occurs  to  one  to  inquire  whether  pentandria  has  been 
derived  from  forbesii  by  the  shortening  of  the  flower  clusters,  or 
whether  pentandria  is  the  more  primitive  form.  In  the  literature  of 
the  subject,  the  only  reference  that  has  been  found  to  a  form,  similar 
to  that  described,  is  by  Andre,  who  mentions  a  variety  as  found  by 
him  in  the  Andes  of  Ecuador,  in  the  identical  garden  where  he  dis- 
covered the  "Chamburo"  form  (see  p.  29).  It  will  be  recalled  that 
this  was  in  a  high  altitude.  He  says  of  this  second  form  that  it  is 
"smaller  with  a  ribbed  fruit  of  a  wholly  new  appearance,"  different 
from  anything  that  he  had  seen  elsewhere.  It  is  there  known  as 
''Chiloacan."  It  seems  not  improbable  that  this  is  identical  with 
the  form  pentandria  which  has  been  described  as  found  in  Hawaii. 
The  high  Andean  altitudes  may  probably  be  regarded  as  the 
home  of  the  form,  for  although  Andre  found  it  in  a  garden,  it  has  not 
been  recorded  from  other  sources  which  can  be  regarded  as  its  native 
habitat.  How  it  came  to  Hawaii  can  not  be  determined,  for  travelers 
from  these  islands  have  brought  or  received  seeds  from  almost  all 
tropical  and  subtropical  countries. 

Forms  8  and  9  may  perhaps  be  regarded  as  the  results  of  the  cross- 
ing of  the  other  forms. 

Form  11,  ernstii.  This  it  will  be  seen  combines  the  characters  of 
the  ordinary  pistillate  and  those  of  the  elongata.  It  is  well-known 
that  seeds  from  the  hermaphrodite  flowers  of  elongata  yield  many 
pistillate  plants  as  well  as  hermaphrodites  and  some  coenomoncecious 
individuals.  It  is  not  surprising  that  a  form  should  be  found  com- 
bining the  female  and  hermaphrodite  characters. 

Form  12.  The  above  remarks  apply  equally  well  to  form  12, 
which  differs  from  the  last  only  in  the  possession  of  staminate  flowers 
which  are  normal  to  hermaphrodites. 

Form  13.  Reference  has  been  made  to  the  manner  in  which  this 
appeared. 

ORIGIN   OF   THE    DKECIOTJS   CARICA  PAPAYA. 

The  dioecious  Carica  papaya,  being  the  one  most  widely  known 

and  described  and  considered  as  the  normal  type  of  the  specie, 

been  the  subject  of  the  most  speculation  and  study  as  to  its 

origin.     As  to  its  native  habitat  it  is  now  generally  conceded  to  be 

of  American  or  Antillean  origin.     Some  writers  have  regarded  it  as 


32 

indigenous  to  Asia  or  Africa,  but  as  De  Candolle,1  Solms-Laubach, 
and  others  have  clearly  pointed  out,  this  view  is  wholly  untenable. 
There  is  no  record  of  its  having  been  known  before  the  discovery 
of  America.  There  is  no  Sanskrit  name  for  it.  The  modern  Indian 
names  for  it  are  derived  from  the  American  word  papaya,  which  in 
turn  is  a  corruption  of  the  Carib  "ababai."  Nevertheless,  the  plant 
was  introduced  into  the  Old  World  at  an  early  date,  for  Watt2  records 
that  seeds  were  taken  from  India  to  Naples  in  the  year  1626.  There 
is  some  difference  of  opinion  as  to  the  locality  of  its  origin.  Correa 
de  Mello  and  Spruce  consider  the  West  Indies  as  its  home,  while 
De  Candolle  includes  also  the  shores  of  the  Gulf  of  Mexico  as  prob- 
ably within  its  native  habitat.  Solms-Laubach  inclines  strongly 
to  the  opinion  that  its  home  has  been  Mexico  and  Central  America. 
On  the  whole  the  continental  origin  appears  more  probable. 

It  is  an  interesting  fact  that  the  species  has  been  found  nowhere 
outside  of  cultivation  except  where  it  appears  to  be  an  escape.  How 
it  came  into  existence  is  a  study  quite  as  interesting  as  that  relating 
to  its  native  habitat.  Solms-Laubach  proposes  the  hypothesis 
that  this  plant  is  the  product  of  the  fusion  of  several  wild  species, 
and  represents  the  product  of  the  ancient  culture  of  Mexico,  although 
not  necessarily  the  result  of  intentional  hybridizing,  but  rather  of 
the  selection  by  man  of  natural  hybrids  showing  valuable  char- 
acters. It  evidently  had  been  in  cultivation  long  before  the  dis- 
covery of  America.  That  some  of  its  near  antecedents  have  been 
either  monoecious  or  hermaphrodite  appears  highly  probable  from 
the  presence  of  an  aborted  pistil  in  the  staminate  flowers  of  the 
male  tree;  from  the  frequent  cases  of  development  of  this  aborted 
organ  into  a  functioning  pistil;  and  from  the  increasing  number  of 
such  hermaphrodite  flowers  under  certain  conditions  of  climate 
and  treatment.  This  tendency  shows  itself  chiefly  in  the  male  tree 
where  all  the  organs  are  present  in  some  form.  In  the  female  where 
the  stamens  have  entirely  disappeared  there  are,  so  far  as  can  be 
learned,  no  recorded  instances  of  such  change  to  hermaphroditism 
taking  place. 

BREEDING   WITHIN  THE   DHECIOUS   FORMS. 

Very  little  effort  has  been  made  to  improve  the  papaya  by  sys- 
tematic breeding.  There  has  been  some  selection  on  the  part  of 
growers  who  naturally  plant  the  seeds  from  particularly  pleasing 
fruits.  The  most  of  such  selection  has  been  with  the  dioecious 
papaya  and  here  there  is  an  inherent  difficulty  even  in  the  way  of 
the  scientific  breeder.  Seed  from  a  pistillate  tree  will  necessarily 
be  a  cross  of  two  individuals.     The  characters  of  the  female  plant 

»  Origin  of  Cultivated  Hants.    London,  1884,  pp.  293-295. 

2  Dictionary  of  the  Economic  Products  of  India.    Calcutta,  1889,  vol.  2,  p.  159. 


33 

may  be  known,  but  those  of  the  male  plant  are  utterly  unknown. 
The  parent  stock  from  which  both  came  may  be  known,  but  since 
there  is  wide  variation  in  the  fruit  of  two  pistillate  trees  from  the 
same  stock  it  is  reasonable  to  suppose  that  there  will  be  the  same 
wide  variation  in  the  male  or  staminate  trees.  The  variation  between 
the  pistillate  trees  can  easily  be  determined  because  their  fruits  are 
in  evidence  and  can  be  tested;  but  the  characters  which  are  inherent 
in  the  male  or  staminate  tree,  and  winch  will  be  transmitted  by  it 
to  its  progeny,  can  be  determined  only  through  the  long  process 
of  actual  hand  pollination,  the  sowing  of  the  seed  thus  produced,  and 
the  testing  of  the  fruit.  Even  then  what  portion  of  its  excellent 
or  indifferent  qualities  may  have  been  inherited  from  its  male  parent 
can  not  be  known.  Furthermore,  the  difficulty  becomes  aggravated 
by  the  fact  that  papaya  trees  usually  degenerate  after  a  few  years. 
At  least  pistillate  trees  usually  fail  to  produce  good  fruit  after  a  few 
years  of  growth,  although  they  may  continue  to  produce  indifferent 
fruit  for  many  years.  Therefore,  even  if  the  inherent  characters 
of  the  male  or  staminate  tree  could  be  determined  with  reasonable 
accuracy,  before  any  such  determination  could  be  made  the  tree 
would  have  become  too  old  to  be  in  a  reliable  state  of  virility  if  it 
degenerates  as  rapidly  as  the  pistillate  tree.  The  new  methods 
of  asexual  propagation  referred  to  on  page  9  will  aid  in  overcoming 
this  difficulty,  but  it  appears  reasonable  to  suppose  that  the  process 
of  producing  a  stable  variety  of  good  qualities  by  the  use  of  this 
dioecious  type  would  be  extremely  long  and  tedious.  The  hope, 
therefore,  must  he  in  the  use  of  a  hermaphrodite  type.  Here  it  is 
possible  to  select  an  individual  of  known  qualities.  This  may  be 
used  as  the  sole  parent  stock  or  may  be  combined  with  another 
parent  of  known  qualities.  What  mixtures  there  may  be  in  the 
individual  at  the  start  may  not  be  known;  but  through  repeated  selec- 
tions and  the  elimination  of  undesirable  characters,  it  should  be 
possible  to  produce  a  reasonably  pure  strain,  provided,  of  course, 
that  the  stock  is  kept  pure  by  constantly  avoiding  cross-pollinations 
with  plants  of  different  characters,  a  process  which  is  necessary  in 
all  plants  reproduced  by  seed  and  whose  flowers  are  subject  to  acci- 
dental cross-pollination. 

A  further  practical  difficulty  in  the  use  of  the  dioecious  type,  from 
the  standpoint  of  the  papaya  grower,  as  well  as  the  breeder,  is  the  fact 
that  a  very  large  proportion  of  the  trees  from  any  given  lot  of  seed  are 
liable  to  be  staminate,  or  males,  and  therefore  useless,  only  a  few  trees 
being  necessary  to  pollinate  all  the  pistillate  trees.  It  is  impossible 
so  far  to  distinguish  the  staminate  from  the  pistillate  trees  in  the 
early  stages  of  their  development.  Therefore,  in  any  papaya  orchard 
planted  with  the  dioecious  type,  a  very  large  percentage  of  the  trees 


34 

must  be  cut  out  after  they  have  grown  almost  to  maturity,  resulting 
in  unevenness  and  irregularity  in  the  orchard  and  much  loss  of  time 
and  space.  For  this  reason,  together  with  the  difficulties  of  breeding, 
the  dioecious  type  probably  will  be  largely  eliminated. 

BREEDING  THE   HERMAPHRODITE   FORMS. 

Turning  to  these  forms  with  more  hope  of  results,  some  experiments 
are  being  conducted.  Here  it  is  possible  to  deal  with  a  single  indi- 
vidual mother  plant.  One  of  the  first  facts  to  be  determined  is  the 
extent  to  which  the  offspring  of  such  a  parent  may  be  expected  to  be 
fruit-bearing  trees.  It  was  known  from  earlier  observation,  with- 
out any  definite  experiment,  that  a  large  number  of  the  seeds  from  a 
fruit  of  a  hermaphrodite  flower,  produce  fruit-bearing  trees,  either 
pistillate  or,  like  the  parent,  hermaphrodite. 

A  tree  was  found  in  a  Honolulu  papaya  orchard  producing  fruit  of  ex- 
cellent flavor.  The  fruit  from  which  the  seed  was  taken  was  of  the  long 
cylindrical  form,  but  it  can  not  be  stated  that  all  the  fruits  on  the  tree 
were  of  that  shape.  Its  flowers  were  staminate  and  hermaphrodite, 
and  so  far  as  observed,  of  the  elongata  form.  The  flowers  had  not 
been  hand-pollinated  and  it  is  therefore  impossible  to  state  whether 
they  were  autogamously  fertilized  or  otherwise.  The  seeds  were 
planted  May  2,  1910,  and  later  35  of  the  young  plants  were  set  in  the 
orchard.  Of  these,  ¥v  34  were  hermaphrodite  and  1  was  a  staminate 
tree.  The  hermaphrodite  flowers  on  most  of  the  trees  were  of  two 
types,  some  of  the  elongata  form  and  others  resembling  pentandria, 
with  corresponding  difference  in  the  fruits.  All  of  the  35  trees  were 
designated  as  No.  2355,  and,  according  to  the  method  adopted  in  all 
our  breeding  work,  the  individuals  were  designated  thus:  2355:1, 
2355:2,  etc.  The  best  of  the  trees  from  the  standpoint  of  uni- 
formity of  cylindrical  shape  in  fruit  was  2355:1,  which  was  also  of 
very  good  flavor  and  a  reasonably  good  producer.  This  was  selected 
for  further  breeding.  Two  of  its  flowers  were  hand-pollinated  each 
with  its  own  pollen  and  protected  from  all  possible  allogamy.  The 
seeds  collected  from  these  two  fruits  were  planted  as  No.  3198. 

At  this  writing  there  are  of  this  F2,  343  trees  living  and  old  enough 
to  have  exhibited  sex  characters,  some  of  them  having  done  so  for 
several  weeks  past.  The  individuals  judged  by  the  characters 
apparent  to  date  are  as  follows: 

Pistillate  trees 98 

Elongata 61 

Pentandria 45 

Elongata,  pentandria,  and  intermediate 55 

Pentandria  and  pistillate 1 

Fruit  bearing  but  not  determinable  in  form 62 

Total  fruiting  exclusive  of  correse 322 


35 

Stamina  te 18 

Correse 3 

Total 343 

It  will  thus  be  seen  that,  exclusive  of  correae,  approximately  94 
per  cent  of  the  trees  are  fruit  bearing.  This  is  an  encouraging  result, 
so  far  as  the  elimination  of  the  males  is  concerned.  It  is  not  prob- 
able that  the  61  designated  as  elongata  will  continue  to  produce 
flowers  and  fruits  of  this  form  exclusively.  It  is  probable  that  some 
of  the  pentandria  form  of  flowers  and  fruits  will  appear,  but  it  is 
hoped  that  it  will  be  possible  to  develop  a  pure  strain  of  uniform 
shape.  It  is  probable  that  the  progeny  will  continue  to  include 
pistillate  as  well  as  hermaphrodite  trees.  Whether  it  will  be  neces- 
sary to  have  two  forms  of  a  variety,  one  borne  on  the  pistillate  tree 
and  another  on  the  hermaphrodite,  can  not  be  determined  at  present. 
If  this  should  be  the  case,  it  would  necessitate,  in  marketing,  two 
packs,  which  might  be  sold  under  different  varietal  names.  This 
will  be  no  serious  disadvantage,  provided  uniformity  can  be  main- 
tained in  each  form.  There  are  two  ways,  however,  in  which  it  is 
conceivable  that  a  uniformity  might  be  maintained,  common  to  the 
hermaphrodite  and  the  pistillate  alike.  Among  the  pistillate  trees 
of  No.  3198  were  several  with  elongated  cylindrical  ovaries,  like 
those  found  on  the  hermaphrodite  elongata,  which  would  indicate 
that  this  particular  shape  of  ovary  and  resulting  fruit  is  not  necessa- 
rily confined  to  hermaphrodites. 

Another  conceivable  means  of  establishing  uniformity  would  be  in 
the  selection  of  pistillate  trees  whose  fruits  are  angular  like  those  of 
the  hermaphrodite  pentandria. 

HERMAPHRODITISM   IN   LYCHNIS   DIOICA. 

In  this  connection  the  experiments  of  Shull 1  on  Lychnis  dioica  are 
interesting  and  important.  Hermaphrodite  individuals  appear  as 
mutants  in  L.  dioica.  These  the  author  concludes  are  modified  males 
and  are  of  two  kinds,  distinguished  as  "genetic"  and  "somatic" 
hermaphrodites. 

"When  the  genetic  hermaphrodites  are  used  as  pollen  parents,  either  when  self- 
fertilized  or  in  crosses  with  females,  their  progeny  consists  of  females  and  hermaphro- 
dites. When  they  are  used  as  pistil  parents  and  fertilized  by  normal  males,  they 
produce  females  and  normal  males. 

Somatic  hermaphrodites  may  be  externally  indistinguishable  from  genetic  her- 
maphrodites, but  when  used  as  pollen  parents  they  produce  no  hermaphrodite  off- 
spring, but  only  females  and  normal  males. 

These  somatic  hermaphrodites,  however,  were  found  to  be  rare  in 
comparison  to  the  genetic  hermaphrodites.     The  author  has  shown 

i  G.  H.  Shull.     Bot.  Gaz.,  49  (1910),  No.  2,  pp.  110-125;  52  (1911),  No.  5,  pp.  329-368. 


36 

in  the  case  of  L.  dioica  that  the  eggs  can  not  transmit  the  hermaphro- 
dite character  to  the  male  offspring.  This  character  can  be  carried 
only  through  the  pollen. 

" Among  the  offspring  of  genetic  hermaphrodites/'  he  continues, 
"were  a  small  number  of  male  mutants,  which  on  breeding  proved 
to  be  normal  males."  In  the  case  of  2355  referred  to  (see  p.  34)  there  is 
one  male  mutating  from  the  hermaphrodite  form  and  much  has  been 
said  of  hermaphrodites*  appearing  as  mutants  from  ordinary  males. 
Such  sex  mutants  appear  to  occur  not  infrequently  in  the  papaya. 

BREEDING  WITHIN  THE   ANDROMONCECIOUS  FORMS. 

Very  limited  experience  has  been  afforded  in  crossing  hermaphro- 
dite flowers  of  the  correse  form  from  trees  of  different  origin.  In  one 
instance  such  a  cross  was  made,  resulting  in  several  pistillate  trees, 
a  few  staminate,  and  many  hermaphrodite  of  the  elongata  form  out 
of  73  trees  in  all.  This  is  interesting  evidence  which  would  appear 
to  indicate  that  elongata  and  correse  differ  only  in  degree. 

Another  result  of  this  cross  is  worthy  of  note.  One  of  the  pistillate 
trees  of  this  progeny  produces  an  ovary  and  a  resulting  fruit  very 
closely  resembling  those  of  elongata  form  (PI.  X,  fig.  2),  which  would 
again  indicate  that  this  shape  of  ovary  is  not  necessarily  confined  to  a 
hermaphrodite  flower. 

CROSSING  THE   DIFFERENT  FORMS. 
POSSIBILITIES   AND   LIMITATIONS. 

It  may  often  be  desirable  to  combine  the  characters  of  individuals 
of  the  different  forms.  To  test  the  possibilities  of  pollinations,  seven- 
teen different  combinations  of  pollen  and  stigma  have  been  tried. 
The  table  (p.  27)  shows  the  number  of  cases  in  which  each  of  these 
combinations  was  tried  in  the  experiment  and  the  number  of  suc- 
cesses resulting.  The  results  of  pollination,  designated  in  the  sec- 
ond column  as  "successful"  and  "unsuccessful,"  will  show  at  a  glance 
whether  any  successes  have  been  attained  in  any  particular  cross. 
Some  of  the  successful  pollinations  have  been  repeated  many  times 
since  the  close  of  this  specific  experiment.  It  should  be  stated  also 
that  the  pollinations  on  any  given  tree  were  not  made  in  a  single  day, 
usually  not  more  than  one  flower  being  available  on  any  one  day. 
This  reduces  the  influence  of-  weather  conditions  which  also  were 
chosen  as  favorably  as  possible.  The  usual  precautions  were  taken 
to  prevent  the  access  of  pollen  other  than  that  designated.  Emascu- 
lation was  practiced  where  required  and  flowers  covered  with  cotton 
sacks  which  had  been  immersed  in  warm  paraffin. 


37 


Table  showing  pollinations  and  result*. 


Pollina- 
tion 
number. 


Successful  or 
unsuccessful. 


First 

Second. . . 

Thir.l.... 

Fourth... 

Fifth 


Sixth.., 


ssful 

Unsuccessful . 

Unsuccessful. 
Successful. . . . 
Unsuccessful . 


Successful- 


Seventh..    Successful. 


Eighth. 


Ninth. . . 


Tenth 


Successful. 


Successful. 


Successful. . 


Peseript  ion  of  pollination. 


Eleventh. 

Successful 

Twelfth.. 

Successful 

T  h  i  r  - 
teenth. 

Unsuccessful 

Four- 
teenth. 

Successful 

Fifteenth 

Successful 

Sixteenth 

Successful 

Seven- 

Successful  

teenth. 

Hermaphrodite  elongata  flower 

with  Its  own  pollen. 
Hermaphrodite  elongate  flower 

with  pollen  from  cf  flower  in 

same  cluster. 
Hermaphrodite  elongata  flower 

with  pollen  from  cf  flower  in 

another  cluster. 
Hermaphrodite  elongata  flower 

with  pollen  from   8.    flower 

from  another  elongata  tree. 
Hermaphrodite  elongata  flower 

with  pollen  from   cf   flower 

from  another  elongata  tree. 

Hermaphrodite  elongata  flower 
with  pollen  from  $  flower  of 
correae. 


Hermaphrodite  elongata  flower 
with  pollen  from  a  cf  flower 
from  male  tree  (form  2). 


Pistillate  tree  flower  with  pol- 
len from  a  8.  flower  from  the 
elongata  tree. 


Pistillate  tree  flower  with  pol- 
len from  a  cf  flower  from  the 
elongata  tree. 


Pistillate  tree  flower  with  pol- 
len from  c?  flower  from  male 


Pistillate  tree  flower  with  pol- 
len from  8  flower  from  a  tree 
of  correae  form. 


Hermaphrodite  flower  of  cor- 
reae with  pollen  from  8.  flower 
of  elongata. 

Hermaphrodite  flower  of  cor- 
reae with  pollen  from  cf  flower 
of  elongata. 

Hermaphrodite  flower  of  cor- 
reae with  pollen  from  cf  flower 
of  male  tree  (form  2). 

Hermaphrodite  flower  of  cor- 
reae with  its  own  pollen  (hand 
pollin 

Hermaphrodite  flower  of  cor- 
reae with  its  own  pollen 
(sealed  in  sack  but  not  hand 
pollinated). 

Hermaphrodite  flower  of  cor- 
reae with  pollen  from  8.  flower 
of  another  correae. 


Tree 
used  as 

pistil 
parent. 


2125:3 
2123:6 

2091:1 
2091:11 

2168:4 


2355:1 
2355:6 

2355:7 
2355:2 

2461:6 

2493:1 

3198:11 

3198:14 

2491:6 

2493:6 

3198:19 

3198:20 

3198:21 

2491:1 

2491:2 

2087:3 

2087:16 

3198:1 

3198:2 

3198:3 

3198:4 

3198:5 

3198:7 

3198:10 

3198:12 

2491:3 

2491:5 

3198:1 

3198:2 

3198:3 

3198:4 

3198:5 

1996:11 

1996:37 

1982:22 

3198:6 

3198:7 

3198:8 

3198:9 

2491:9 

2191:11- 

3198:12 

3198:16 

3198:17 

3198:18 

2461:15 

2476:9 

3198:13 

3198:15 

2459:1 

2493:2 

2494:5 

2494:7 

2979:1 

2174:3 

2474:4 

2474:10 

2979:3 

2474:12 

2471:13 

2979:2 

1996:27 

2494:5 

2979:2 

3198:15 

2090:6 


Number 
of  flowers 
polli- 
nated. 


Number 

of  fniits 
set. 


Number 

of 
failures. 


2 

2 

2 

2 

2 

2 

1 

1 

1 

1 

2 

2 

2 

2 

3 

3 

1 

1 

U 

l0 

6 

l0 

3 

3 

2 

2 

1 

1 

2 

2 

11 

1 

R 

0 

2 

1 

6 

s 

is 

0 

27 

0 

23 

0 

24 

0 

- 

0 

23 

3 

2.-, 

3 

21 

2 

8 

0 

u 

0 

21 

1 

8 

1 

1 

1 

4 

0 

i 

7 

1 

1 

1 
1 

7 
5 

22 
33 
0 
2 
26 
18 
0 
0 
0 
25 
14 
0 
0 
0 
0 
2 
0 
0 
1 
0 
1 
23 
10 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
11 
6 
0 
0 
0 
0 
10 
8 
1 
1 

IS 
27 
23 
2 
8 
20 
22 
22 
8 
16 
20 
7 
0 
0 
4 
0 
0 


1  It  was  later  discovered  that  the  flowers  of  these  trees  failed  to  become  fecundated  with  any  pollen  that 
was  tried  artificially. 


38- 

From  the  data  contained  in  the  above  table  it  is  possible  to  draw 
some  conclusions  and  to  point  to  other  probabilities  indicated.  It 
will  be  observed  that  the  only  pollinations  which  were  wholly  unsuc- 
cessful were  Nos.  2,  3,  5,  and  13.  These  were  in  every  case  examples 
of  the  use  of  pollen  from  the  staminate  flowers  of  the  elongata  form 
and  include  all  such  cases  except  the  ninth  class  of  pollination.  In 
the  ninth,  where  pistillate  flowers  of  different  individuals  of  No.  3198 
received  such  pollen,  fertilization  took  place.  This  pollen  was  all 
taken  from  one  tree,  and  the  instance  constitutes  the  only  case  on 
record  at  the  station  where  pollen  from  the  staminate  flowers  of 
elongata  was  successful  in  fertilization.  It  seems  probable,  there- 
fore, that  the  stamens  of  such  flowers  in  most  trees  are  infertile.  In 
the  earlier  work  on  the  papaya  here  these  indications  had  not 
developed,  and,  believing  the  staminate  to  be  functioning  flowers, 
this  elongata  form  was  spoken  of  as  monoecious.  While  the  above 
results  show  that  this  was  a  correct  supposition  for  at  least  the  one 
tree  from  which  pollen  was  taken  to  No.  3198,  so  many  examples  of 
the  failure  of  such  pollen  are  on  record  here,  that,  at  least  for  the 
present,  elongata  must  be  described  as  usually  hermaphrodite. 

A  further  fact  brought  out  by  the  figures  of  the  table  is  that  certain 
individuals  and  stocks  exhibit  peculiarities  of  their  own  in  relation  to 
pollination.  The  stocks  of  Nos.  2491,  2493,  and  2494  were  not  fer- 
tilized with  any  pollen  that  was  applied  to  them,  except  in  the  case 
of  2494 : 5,  which  was  fertilized  by  its  own  pollen  within  a  sack.  This 
individual  peculiarity  was  not  discovered  in  the  earlier  experiments 
which  seemed  to  indicate  that  the  seventh  and  the  eleventh  classes  of 
pollinations  were  not  successful.  The  later  experiments  have  shown 
that  the  failure  of  the  earlier  trials  was  due  to  such  peculiarities  of 
stocks  or  of  individuals.  The  presence  of  these  peculiarities  suggests 
great  caution  in  generalizing,  and  results  presented  here,  as  in  the 
case  of  the  earlier  reports,  are  offered  merely  as  cumulative  data. 

However,  it  is  evident  that  any  of  the  forms  may  be  crossed. 
What  the  results  will  be  in  the  sex  characters  of  the  offspring  has  been 
determined  only  in  part.  If  the  breeding  is  confined  to  the  purely 
dioecious  forms,  there  are,  so  far  as  the  records  show,  no  instances  of 
the  appearance  of  truly  hermaphrodite  forms  by  sudden  mutations. 
Hermaphrodite  flowers  may  appear  among  the  staminate,  thus  giving 
rise  to  andromonoecism,  as  has  been  stated. 

COMBINING   DIOECIOUS   WITH   HERMAPHRODITE    FORMS. 

Although  it  is  best  in  practical  papaya  culture  to  avoid  the  dioecious 
varieties  for  reasons  that  have  been  pointed  out,  it  is  nevertheless 
true  that  some  of  these  have  highly  valuable  characters  which  it 
would  be  desirable  to  introduce  into  a  hermaphrodite  form.  Obvi- 
ously in  any  cross  which  is  to  combine  in  part  the  characters  of  indi- 


39 

viduals  of  these  two  forms,  the  pollen  must  be  taken  either  from  the 
staminate  tree  to  the  hermaphrodite  flower  or  from  the  hermaphro- 
dite flower  to  the  pistillate  tree.  That  is  to  say,  the  seventh  or  eighth 
type  of  pollination  must  be  employed.  There  is  objection  to  the 
seventh  on  the  ground  that  it  employs  a  male  parent,  many  of  whose 
characters  are  unknown,  because  it  bears  no  fruit,  and  further  because 
the  hermaphroditic  character  would  probably  be  lost.  In  this  latter 
particular  the  experiments  have  not  been  carried  far  enough  to 
determine  the  sex  characters  of  the  offspring  of  such  a  cross  for  the 
reason  that  the  first  attempts  to  impregnate  the  ovary  of  the  herma- 
phrodite flower  with  pollen  from  the  male  tree  resulted  in  repeated 
failures,  for  reasons  which  have  been  referred  to  (see  p.  38).  Since 
the  hermaphrodite  is  apparently  a  modified  form  of  the  male,  or 
vice  versa,  it  would  not  be  surprising  to  find  that  sex  results  in  this 
cross  would  correspond  rather  closely  with  those  which  Shull  has 
found  in  Lychnis  dioca.  Should  that  prove  to  be  true,  no  herma- 
phrodites would  result  from  such  a  cross,  unless  it  be  as  an  occasional 
mutant. 

If  this  be  the  case  there  would  remain  the  other  alternative,  viz, 
to  use  the  hermaphrodite  flower  as  the  male  parent,  applying  its 
pollen  to  a  pistillate  tree  of  known  characters.  No  experiments  of 
this  kind  have  been  completed  in  which  a  pistillate  tree  of  purely 
dioecious  origin  has  been  used.  A  similar  experiment  in  which  a 
pistillate  tree  from  hermaphrodite  stock  was  used  as  the  female 
parent  is  interesting.  It  is  possible  that  results  would  not  be  differ- 
ent had  the  pistillate  tree  been  of  pure  dioecious  stock.  Seeds  were 
collected  from  a  chance  fruit  of  unknown  origin  and  planted  as  No. 
2087.  The  fruit  was  chosen  purely  for  its  flavor  and  other  pleasing 
qualities,  and  not  with  a  view  to  the  specific  experiments  which  later 
developed.  Seventeen  trees  were  planted  out  when  too  young  to 
exhibit  sex  characters.  These  developed  into  12  pistillate  trees,  4 
hermaphrodite,  and  1  staminate.  When  they  came  into  bearing  No. 
20S7 :3  9  was  crossed  with  No.  2087 :  17  $  .  The  Ft  from  this  cross  was 
planted  under  accession  No.  2491.  At  the  time  the  trees  were  exam- 
ined there  were  5  pure  pistillate  individuals,  9  with  more  or  less 
tendency  to  hermaphroditic  characters,  and  1  staminate.  The  latter 
produced  only  staminate  flowers.  Of  the  9,  there  was  one  normal 
hermaphrodite  of  the  elongata  form,  and  another  the  same  except  in 
the  case  of  two  fruits.  The  remainder  exhibited  flowers  and  fruits 
of  varied  form,  some  with  the  stamens  reduced  to  five  in  number,  and 
producing  fruit  of  the  pentandria  form.  In  others  certain  of  the 
carpels  failed  to  develop  in  the  fruit,  due  to  defective  stigmas,  thus 
giving  rise  to  gibbous  fruits.  The  stigmas  and  the  anthers  were  both 
inclined  to  irregularity  of  position,  anthers  being  found  on  the  carpels. 


40 

Fruits  of  elongata,  of  pentandria,  and  of  various  other  forms  could  be 
found  upon  the  same  tree. 

A  similar  cross  was  made  between  2087:16  $  and  1191:1  5  (elon- 
gata).  The  seeds  resulting  from  this  cross  were  divided  into  two  lots 
on  the  basis  of  color  and  were  planted  as  2493  and  2494,  the  former 
being  gray  and  the  latter  black.  The  resulting  population  in  the 
case  of  2493  presented  11  pistillate,  1  normal  hermaphrodite  of 
elongata  form,  3  abnormal  hermaphrodites  like  those  described  in  the 
last  cross,  3  males  (nonfruit-bearing),  and  1  hermaphroditic  male. 
The  individuals  of  2494  were  6  pistillate,  1  male,  and  2  hermaphroditic 
males. 

The  above  figures,  representing  results  in  sex,  are  to  be  understood 
as  applying  to  the  trees  which  were  planted,  there  being  in  nearly 
every  case  many  more  trees  than  space  could  be  found  to  plant. 

STOCKS   NOT   SHOWING   ANY   FERTILIZATION. 

A  noteworthy  fact  developed  in  regard  to  the  stocks  of  2493  and 
2494,  as  referred  to  above.  The  flowers  of  a  number  of  the  different 
pistillate  and  hermaphrodite  trees  were  hand-pollinated  with  pollen 
from  different  sources,  but  in  every  instance  failed  to  develop.  The 
pollen  used  in  these  instances  was  taken  from  the  hermaphrodite 
flowers  of  correse,  from  pure  staminate  trees,  and  from  hermaphrodite 
and  supposed  staminate  plants  of  the  elongata  type. 

PARTHENOCARPY. 

Some  of  these  trees  were  found  to  be  capable  of  a  parthenocarpic 
development  of  fruit.  Certain  pistillate  flowers  were  covered  with 
paraffined  sacks  to  prevent  pollination  and  developed  within  the  sacks 
until  the  latter  were  broken  by  the  force  of  growth.  Such  fruits  were 
found  to  be  seedless.     One  of  these  is  illustrated  in  Plate  IX,  figure  2. 

A  further  peculiar  fact  is  that  these  trees  if  not  operated  upon  in 
any  way  received  pollen  from  some  source  which  satisfied  their  needs 
and  resulted  in  seed  production.  That  the  failure  of  those  hand- 
pollinated  was  not  due  to  errors  of  technique  seems  certain,  since  the 
method  and  the  time  were  the  same  as  were  used  successfully  in  so 
many  other  cases  with  flowers  of  the  same  external  structure. 

A  tree  in  the  Mount  Tantalus  orchard  of  the  station  was  found  to  be 
producing  seedless  fruit.  This  is  a  pistillate  tree  of  hermaphrodite 
stock.  On  one  occasion  six  fruits  were  cut  open  and  found  to  be 
without  any  seeds.  On  another  occasion  seven  were  cut  open  and 
all  were  seedless  except  one  which  contained  three  seeds.  Several 
of  the  flowers  were  covered  in  paraffined  sacks  and  were  hand-polli- 
nated when  the  stigmas  appeared  to  be  ready  for  the  reception  of 
pollen,  the  sacks  being  again  put  over  the  flowers.  Several  other 
flowers  on  the  same  tree  were  covered  with  the  sacks  and  left  without 


41 

any  pollen.  All  of  those  flowers,  pollinated  and  unpollinated  alike, 
produced  fruit  but  no  seed.  Those  unpollinated  furnish  another 
clear  case  of  parthenocarpy.  In  the  case  of  those  that  were  hand- 
pollinated  the  pollen  appears  to  have  been  wholly  without  influence, 
being  in  this  respect  unlike  those  of  Nos.  2491,  2493,  and  2494,  referred 
to  above.  It  is  also  fair  to  conclude  that  seedlessness  in  this  tree  was 
not  due  to  a  lack  of  fertile  pollen,  because  pollen  was  actually  applied 
to  the  stigmas,  and  also  because  an  abundant  supply  of  effective  pollen 
was  present  in  the  orchard,  as  evidenced  by  the  presence  of  many 
seeds  in  the  fruits  of  other  trees. 

Other  instances  of  parthenocarpy  in  papaya  have  been  observed. 

Xo.  1996:37,  a  pistillate  tree  of  a  dioecious  stock  whose  male  trees 
showed  some  tendency  to  bear  hermaphrodite  flowers,  exhibited  this 
phenomenon.  Several  of  its  flowers  which  were  sealed  in  paraffined 
sacks  to  prevent  pollination  grew  into  normal  fruits  and  after  three 
months  were  cut  open  and  found  to  be  seedless.  On  the  same  tree 
other  fruits  from  flowers  which  had  not  been  sealed  were  found  to 
contain  many  seeds.  It  is  apparent  that  the  carpels  of  these  flowers 
were  capable  of  development  with  or  without  the  influence  of  pollen. 

In  the  above  it  will  be  observed  that  the  fourteenth  and  fifteenth 
pollinations  proved  successful  in  only  a  few  cases.  It  is  to  be  noted 
that  the  mother  trees  in  all  these  instances  were  of  the  No.  2474  stock? 
which  was  the  progeny  of  the  No.  1996  stock  which  exhibited  the 
tendency  to  parthenocarpy,  although  it  did  not  refuse  pollination. 
This  suggests  the  tr admissibility  of  parthenocarpic  tendencies. 

It  is  apparent,  therefore,  that  parthenocarpy  is  not  rare  in  the 
papaya,  but  that  it  is  not  the  rule  is  proved  by  a  large  number  of 
observations  and  experiments.  Pistillate  flowers  of  most  papaya 
trees  will  fail  to  set  fruit  if  prevented  from  receiving  pollen. 

PARTHENOGENE  SIS. 

Cases  of  parthenogenesis  have  been  watched  for  but  none  has  been 
recorded.  In  one  instance  where  no  pollen  came  in  contact  with  the 
stigma  the  fruit  was  found  to  contain  one  seed,  but  this  proved  to  be 
infertile. 

HYBRIDIZATION   OF   CARICA. 

Ic  is  probable  that  there  has  been  considerable  hybridizing  of 
Carica  by  natural  means  and  the  genus  has  not  been  wholly  neglected 
by  plant  breeders.1  C.  cundinamarcensis  has  been  crossed  with  the 
pollen  of  C.  papaya.  Also  C.  cauliflora  as  a  mother  plant  has  been 
crossed  with  C.  papaya.  Van  Volxem2  crossed  C.  erythrocarpa  with 
the  pollen  of  C.  cundinamarcensis  and  then  proceeded  to  inbreed  by 
crossing  his  new  hybrid  as  a  mother  plant  with  C.  cundinamarcensis. 


I  cf.  Solms-Laubach  and  also  Andre  in  articles  referred  to  above. 
*  J.  van  Volxem.    Gard.  Chron.,  n.  ser.,  14  (1880),  p.  729. 


42 

C.  papaya  has  been  hybridized  with  C.  gracilis,  the  latter  as  the  male 
parent.  In  the  orchards  of  the  Hawaii  station  there  are  trees  which 
are  believed  to  be  natural  hybrids  of  C.  papaya  and  C.  peltata.  At- 
tempts made  at  this  station  to  cross  C.  papaya  with  C.  quercifolia 
have  failed. 

AN   ATTEMPT   TO   BREED   A   HERMAPHRODITE    PAPAYA. 

Mr.  John  Scott,1  who  had  observed  plants  apparently  of  the 
forbesii  form  but  had  not  seen  those  of  elongata  or  pentandria,  was 
impressed  with  the  idea  that  it  would  be  possible  to  increase  the  num- 
ber of  hermaphrodite  flowers  and  shorten  the  peduncles  until  a  truly 
hermaphrodite  race  would  be  attained.  The  work  was  begun  but 
was  unfortunately  terminated  by  the  early  death  of  Mr.  Scott. 

IDEALS   IN   BREEDING  THE    PAPAYA. 

There  seems  to  be  no  good  reason  to  doubt  that  it  will  be  possible  to 
breed  a  papaya  combining  at  least  many  of  the  most  desirable  characters 
and  to  hold  the  variety  reasonably  stable  by  the  same  means  as 
are  employed  in  maintaining  seed  varieties  of  vegetables  and  garden 
flowers.  This  presupposes  segregation  or  hand  pollination  in  either 
case,  the  latter  being  the  method  which  most  breeders  will  be  com- 
pelled to  follow  because  of  the  proximity  of  other  varieties  over  which 
they  have  no  control.  The  simplicity  of  hand  pollination  in  the 
papaya  and  the  large  number  of  seeds  resulting  from  one  operation 
renders  it  a  very  practical  means  even  for  commercial  seed  produc- 
tion. 

It  may  be  well  to  outline  here  some  of  the  ideals  which  the  breeder 
should  have  in  mind  in  his  search  for  Mendelian  characters  which  may 
be  combined. 

1.  Vigor  of  tree. — It  is  important  with  the  papaya,  as  with  other 
species,  to  use  vigorous  individuals  as  parent  stocks. 

2.  Early  and  low  fruiting  habits. — There  is  a  wide  variation  in  the 
plants  in  this  respect,  some  producing  no  fruit  on  the  first  five  or  six 
feet  of  the  stem,  while  others  bear  fruit  which  almost  touches  the  soil. 
It  is  believed  that  this  is  a  character  which  may  be  transmissible,  and 
the  advantage  of  early  and  low-bearing  trees  is  obvious. 

3.  Freedom  from  the  branching  habit. — Trees  that  produce  side 
branches  freely  require  considerable  pruning  to  prevent  the  numerous 
new  shoots  from  taking  the  nourishment  which  should  go  to  the  fruit. 

4.  Productivity  but  not  excessive  bearing. — Trees  that  have  long  bare 
spaces  on  their  stems  and  those  whose  fruits  are  so  numerous  as  to 
crowd  each  other  should  be  avoided  in  favor  of  such  as  have  the  fruits 
well  spaced  with  just  sufficient  room  to  mature  normally. 

i  Trans.  Bot.  Soc.  Edinburgh,  If  (1873),  pp.  287-288. 


43 

5.  Hermaphroditism. — The  reasons  for  preferring  hermaphrodite 
stock  have  already  heen  pointed  out.  The  stocks  may  continue  to  be 
gynodicecious1  and  to  a  very  limited  extent  even  trioecious,2  but  the 
number  of  male  trees  can  be  kept  very  small. 

6.  Suitable  size  in  fruit. — The  size  that  will  be  most  desirable  will 
depend  upon  the  purpose  to  which  the  variety  is  to  be  put.  For 
home  use  or  for  the  fresh  fruit  market  the  extremely  large  varieties 
are  not  popular,  and  the  breeder  of  table  varieties  will  not,  therefore, 
attempt  to  originate  such  forms.  On  the  other  hand  there  is  a  place 
for  these,  if  the  fruit  is  to  be  grown  as  feed  for  poultry  or  other  live 
stock.  For  papain  production,  other  things  being  equal,  the  large 
fruit  would  be  best. 

7.  Yield  in  papain. — Where  the  production  of  papain  is  made  an 
industry  there  can  be  little  doubt  that  the  average  yield  of  this  drug 
could  be  very  greatly  increased  by  judicious  breeding. 

S.  Uniformity  of  shape. — The  breeder  must  seek  to  establish  varie- 
ties in  which  there  will  be  reasonable  uniformity  of  shape  as  well  as 
symmetry  and  smoothness.  It  is  not  necessary  that  all  varieties 
be  alike,  but  there  must  be  uniformity  in  pack.  In  breeding  from 
hermaphrodite  trees  there  will  be  a  large  number  of  pistillate  trees  in 
the  offspring.  Although  the  long  form  is  not  necessarily  confined  to 
the  hermaphrodite  tree,  as  pointed  out  above  (see  p.  34),  nevertheless 
pistillate  trees  do  not  usually  yield  fruit  of  this  shape.  For  this 
reason  the  breeder  may  think  it  best  to  work  for  two  forms  of  fruit — 
the  long,  tending  to  cylindrical,  for  the  hermaphrodite,  and  the 
obovoid  for  the  pistillate.  The  fruits  of  such  an  orchard  would  be 
packed  as  two  varieties. 

9.  Uniformity  in  ripening. — This  is  an  important-  consideration. 
Some  papayas  ripen  and  decay  at  the  outer  end  or  the  point  while 
the  inner  half  near  the  stem  is  too  green  to  be  eaten.  The  ideal 
papaya  in  ripening  shows  its  first  yellowing  along  the  ribs  about 
midway  of  the  fruit  and  ripens  uniformly  toward  each  end. 

10.  Coloring  before  softening. — Some  fruits  ripen  with  very  little 
color,  while  others  acquire  a  beautiful  golden  yellow  when  still  hard, 
and  may  be  kept  for  several  days.  The  latter  are  so  much  more 
attractive  on  the  table  and  in  the  market  that  they  should  be  sought 
after  in  breeding. 

11.  Color  of  flesh. — Those  of  pale  whitish  flesh  must  give  place  to 
the  fruits  of  yellow,  pink,  or  red  color  within.  Recently  some  have 
been  grown  at  this  station  with  a  quite  decidedly  reddish  hue. 

1 2.  Easily  separable  placenta. — If  the  placenta  adheres  tightly  to  the 
inner  portions  of  the  fruit  and  is  more  or  less  buried  in  the  flesh,  it  is 
difficult  to  remove  the  seeds  without  marring  the  appearance  of  the 

1  Containing  hermaphrodite  and  pistillate  individuals. 

2  Containing  hermaphrodite,  pistillate,  and  staminate  individuals. 


44 

fruit.     On  the  other  hand,  it  is  a  distinct  advantage  if  the  placenta 
and  seeds  can  be  readily  removed  without  scraping  the  flesh. 

13.  Flavor. — This  is  without  doubt  the  most  important  factor  to 
be  considered.  Experience  has  shown  that  specific  flavors  can  be 
transmitted,  and  this  affords  the  breeder  an  opportunity  to  originate 
and  establish  varieties  of  high  quality.  This  flavor  can  not  well  be 
described,  but  is  easily  recognized  and  appreciated. 

14.  Keeping  qualities. — The  ideal  papaya  should  be  a  good  keeper, 
and  this  character  has  been  found  often  enough  in  the  fruit  of  indi- 
vidual trees  to  lend  much  encouragement  to  the  breeder. 

INSECT  PESTS. 

By  D.  T.  Fullaway. 

Insect  pests  give  little  trouble  in  papaya  cultivation.  About  the 
only  harmful  insects  noted  on  this  valuable  fruit  tree,  in  the  course 
of  several  years  that  it  has  been  grown  continuously  in  large  numbers 
on  the  station  grounds  and  almost  daily  under  observation,  is  a  red 
mite  {Tetranychus  sp.),  which  occurs  in  small  and  very  scattered 
colonies  on  the  underside  of  the  leaves  and  occasionally  in  excessively 
large  numbers  on  the  fruits,  and  a  caterpillar  (the  larva  of  the  recently 
introduced  moth  Cryptoblabes  aliena),  which  feeds  under  a  web  on 
the  floral  stems  and  beneath  the  flower  clusters  of  this  and  many 
other  economic  trees  and  plants.  Neither  insect  is  injurious  in  the 
sense  of  seriously  affecting  the  crop  of  fruit  for  which  the  plant  is 
grown.  The  mite  would  probably  be  serious,  but  it  seems  to  be 
held  in  check  by  the  many  predaceous  enemies  of  the  small  leaf- 
infesting  forms  which  are  common  on  imported  economic  plants. 
Some  of  the  armored  scales,  like  Saissetia  nigra,  are  occasionally 
found  on  the  trunk  and  foliage,  but  only  incidentally.  Cutworms 
(Agrotis  ypsilon)  also  occasionally  attack  seedling  plants,  but  this 
pest  is  so  easily  controlled  in  the  case  of  the  papaya  that  it  is 
almost  negligible  as  a  factor  in  papaya  cultivation. 

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